AIBU not to want to look after one year old while parents are abroad for 4 d.

Just do it. The co sleeping will have stopped by then. Yes it'll be tiring but rewarding too. I found a similar experience hard work at the time but I missed him so much when he eventually went home.
Actually, just by asking this question, it seems like you don't want to do this. What are the risks if you say no? Your relationship with your DD will be affected. How would you feel about that?

X posts GagaJo. Not Spain then!

4 days with a baby is a big ask. What if he becomes unwell with a high temperature? I’d worry because it’s a huge responsibility. Not so bad if you have backup?

I didn’t spot the reference to Spain either!

Sounds nice, though, in May.

It could be Iceland of course!

Dunno WHERE I got Spain from Callistemon.

I would definitely ask what the sleeping and breastfeeding arrangements are, for a start, and would say no if there are no plans to change the current night time routine.

Is it Spain? I must have missed that.

4) Going with them and looking after him while they are at the wedding sounds like a good idea, GagaJo

I think you should agree on the CONDITION that the co-sleeping and breast feeding have stopped by then. There are 3 months for them to resolve those issues. Switch to a bottle at night as a half-way measure maybe?

That way, you're being REALLY helpful but still making sure you can actually keep the little lad happy while he's at yours. No one would want him to be miserable, not even his mum.

That way, she can either chose to make it workable .

Options:

1) GO to the wedding with him having stopped breastfeeding and cosleeping so he can stay with you.
2) Take him and have him looked after by someone for the day of the wedding.
3) Not go.
4) Maybe take you, pay for you, and you can have him daytime in Spain, while he sleeps with her at night (plus you get a free hol!).

4 would be MY choice!

Do you know what?

I know SAHM or D are looked down on by some and are considered economically inactive but, if they can afford to stay at home, they are doing an invaluable job.

I know many can't afford to. But the thought of leaving a baby crying at nursery would upset me so much although he will probably settle.

I think it is very reasonable for you to ask whether the co-sleeping and breastfeeding will have stopped by then, after all this will play a major part in how he reacts to staying with you for four days and nights.

I really don't know why parents tiptoe around adult children when such a big favour has been requested.

a tricky one.

Presumably your DD will stop breastfeeding by then but, if she wants to continue, perhaps she could ask if they can take the little one to the wedding - many people specify no children but a child being breastfed could be an exception.
However, he will be 17 months or so by then and if she has gone back to work, probably weaned.

How far away is the wedding, can they go just for a couple of nights and how do you feel about the responsibility? Do you have backup?

He will probably be absolutely fine but be prepared to find things to distract him if he frets.

I know how you feel! And four days is quite a long time.