AIBU or are they?

Bashful
You are not the unreasonable one, they are!!
They need to know that your son and his DP can do things their own way, when they're ready to. But I get the feeling they haven't let go of their 'child' and the child is still hanging onto the apron strings, in which case your son may be allowing them to do things 'their way' in order to keep the peace!
Also, it may be their way of trying to help out knowing their child doesn't pay anything (which DP really should, as it is a partnership).
I think you should make time with your son to discuss what's happening, and this is not interfering. Tell him you're worried he's being taken advantage of and you'd like his views on the situation. He may want some help but not know who to ask, or how!
He may welcome your views, but he could also just tell you you're overreacting, but you definitely need to have a personal chat with him!!

They seem to be very over protective but probably mean well. It is probably not good for your son that they are doing all this, not good for his self esteem or motivation,either. I would keep right out of it because sooner or later there will probably some resentment coming in .

Thanks all.

This post caused me some confusion, especially working out what DP meant? (I am guessing it means ^Darling Partner^)

You say "His DP’s parents - they have taken over quite a bit, insisting on doing things that need doing in his house. Granted, his DP asked them to. When they said they would do it, my son said that ...No, he would do it when he felt ready and had the time. They then insisted and basically took over. My son seems to be letting them walk all over him and I have said nothing because I feel as an adult, he needs to sort it out himself. It’s his business and not mine.
However, they have suggested that I could help by doing what his DP suggested. I already offered help to my son ages ago concerning the same thing but he said no he would do it.
I feel a bit insulted and feel they are taking over how my son should run his life. AIBU or are they?

There seem to be two camps here - you and your son versus his partner and their parents, two completely different power hierarchies - and believe me, there is a power struggle going on here.

I suspect that your son's partner would like to have things done around the house that your son for some reason doesn't want to do. Her parents are aware of this and ready and willing to do them, so she has either called on their help as more powerful people than her, or they have stepped in themselves, again feeling themselves more powerful than this young whippersnapper who isn't providing a home fit for their daughter.

In his own house, power should be shared equably between your son and his partner, not reinforced on one side by intervention by outsiders. You know that and have been practising it, but her parents don't, and are still treating her as their helpless little lamb.

At some point your son is going to have to rebel, and tell his "inlaws" a few home truths. That may cause a rupture with them, and potentially the end of his relationship with their daughter. I reckon he needs to do it soon, and tactfully, before he disappears completely into their shadow.

He also needs to do some of the things that he has been putting off, if they are important to his partner. Even taking on one thing would be showing willing. Perhaps you could mention to him (and to the inlaws if the subject comes up again) that you would be happy to help him if he wanted you to and specifically asked you to but it is his home and you would never interfere with his and his partner's plans.

(posted too soon.)They expected the co 'in-laws' to match their support, which created some tension.
Stand firm if they raise the matter with you, and tell them why directly.
Equally, I sympathise: one of my children is living very happily with a partner who for various reasons won't commit to marriage; my worry is that there is no security in terms of the home, which belongs to the partner. I say nothing.

I had a very dear friend, sadly now dead, who acted in exactly the way the girlfriend' parents do, for what she saw as the best possible reasons; she and her husband rushed to do far too much for their adult children in terms of both practical help (decorating, gardening etc) and financial assistance. Their adult children were far too dependent on them, and it did cause some friction with the parents of their partners, who felt as you, (and I) do, that adult children should be more responsible for themselves.

What exactly have the parents been doing and what exactly are they saying you should be doing? Some examples would be helpful to understand things better though they do seem very domineering and I wouldn’t want them as my in-laws. Also you say they are a different generation, are you a lot older than them? I assume you’re a lady or if they expect you to do work are you a gentleman? Sorry just trying to get a feel for things not prying or being rude.

Your follow up posts give more information so I'll change what I said! I think it's a clash of personality and way of life. Of course you don't have to do what they are telling you to do. Luckygirl has the perfect answer. Just repeat as often as required. I hope things settle down for you.

No you are nbu,you did exactly what your ds said when you offered to help.

No you are not being unreasonable Bashful. It's up to you what you do to help and when that help is given. Either Luckygirl's or Kamiso's suggested responses are the way to go.

Espee - it’s difficult to know these days whether something is temporary or not as many choose not to get married. It doesn’t mean that they aren’t committed to each other.
In the past I’ve asked my son if she is, “The One,” and he replied, “I don’t know.”

Blossoming - thank you, those were my thoughts. Nice to have them confirmed.

Lucky girl - great response thank you. I need to be more assertive.

Esspee

Luckygirl's response is perfect.

I note your son isn't committed enough to the relationship to marry the woman. Frankly I would consider her as a temporary girlfriend.

I’d question that conclusion, sorry, I know two couples who are now grandparents but they never married !

They sound very pushy bashful and very cheeky to try and tell you what to do. luckygirl has the perfect answer.

Well beck - no-one is contributing money in this situation. Also, the work done is not DIY/ home improvements because it is a rented house.
As a matter of fact I like the DP very much and think she is a good influence on my son. I don’t know her parents too well yet though. They are a different generation from us and seem to think they should do everything for the couple rather than take a step back to let them lead their own lives and only ask for help if necessary. They just seemed to arrive, take over and volunteer opinions on the way my son, my husband and I lead our lives. They are pleasant enough otherwise.

Luckygirl's response is perfect.

I note your son isn't committed enough to the relationship to marry the woman. Frankly I would consider her as a temporary girlfriend.

i presume they are lending/giving their child some money towards buying a house, and are suggesting you do the same for your son to increase their joint purchasing power.
it's up to you.
what is the relevance of saying that your son's partner has not contributed to the costs of living with him.
this is not really your business.
you seem far too involved in his private business.
as for the other parents, you don't have to take orders from them. if your son hasn't asked you for help, it's up to you want you want to do. you obviously do not like the partner or their parents, so perhaps you are hoping this union will not last, and don't want to encourage it, make it more permanent by buying property together ?
do what suits you.

What luckygirl said

This seems an odd situation to me. Your son rents his house yet is doing work to it, which is surely the responsibility of the landlord. His partner, who apparently makes no contribution to the household expenses is demanding improvements and her parents are attempting to pressure their daughter's partner's mother into contributing to the improvements.
The point is, neither your son nor his partner will benefit financially from the improvements as it is not their property, and it is certainly not the place of the partner's parents to interfere at all, and certainly not to tell you what to do.

It is quite unreasonable for your son's partner's family to ask you to do work on the son and DP's house. If they want to do things to the house themselves that is their choice, but they are over stepping the mark if they ask you to do work as well.

If your son is happy for them to take over then, as you say, that is his choice.

If they ask again, make it clear that you think that as your son is a grown man, he should be capable of looking after his own house, if there is the odd job he needs assistance with you will help if you can, but you are not prepared to do work he and his partner can quite easily do for themselves.

I think a line in the sand needs to be drawn now, before they pull you into doing more and more.

Anyway, it is a rented house. Does the landlord know, and has he given permission for them to do work on his house. When I owned a buy to let, I would have taken exception to a tenant doing work on the property and would expect them to get my permission before doin anything.

The DPs parents, if they are so keen, should rather put all the money they are expending into a fund to help them to buy their own house.

Bashful, do you mean that they are physically and financially helping them out? I don’t see a problem there. If his DP’s parents have the wherewithal to help, I say, why not? Both my sons’ in-laws do a lot in the house, painting,decorating etc etc. I don’t do a thing, except babysitting occasionally. I hope I’ve understood the situation correctly .

No you most certainly aren't! It's a bit cheeky of them imv.

If the parents ask you again just say something along the lines “I wouldn’t dream of interfering as XXXX is very independent and wouldn’t want me to ?????”

It does get a bit trickier once in-laws/different families come into the equation. Not really a case of being right or wrong just different ideas on parenting and expectations.