Advise

I have found that between my oldest grandkids and my newest one, things have changed especially on weaning. I had to really bite my tongue when my DD started baby led weaning I was convinced my DGS would choke. I only kept quiet as DD went to a special course on it. Now DGS eats so well and as nothing has to be pureed, so easy to feed out and about. He just eats what we eat. Give MIL time and lots of information and she will hopefully come round to understand that things have changed. Good Luck and enjoy your baby.

You sound a delightful girl. You have oodles of common sense and are very empathic. Your confidence will grow and you will speak with more authority as the months go by on any issue relating to your son. Your kindness to your MIL does you credit. As she sees you grow in confidence, she will know the little one is safe and sound and will be able to relax and enjoy the family dynamic without the need to 'helicopter granny' her precious little grandchild. It will all work out fine. Just be assertive without being aggressive. Good luck.

Could you find an up to date book, or print some pages from the internet, outlining the current practices? You could go through them together in a relaxed way and let her take them home.
You are fortunate to have such a loving GM for your child, and she is lucky to have such a caring DIL in you, but you must insist that she follows the rules

32 years ago I followed the advice and put my son to sleep on his tummy.
Advice changed and I was just as aware of that change as DD was, accepted the statistics and never once tried to do things 'the old way'.
I believe OP must explain in the kindest possible way that she doesn't want this to become a source of stress and please would MiL just go along with it.
Popping in is a lovely way to sustain the relationship but maybe cut back a bit as you build your own social circle.

I’m new to being a mil and a gran, so I can only advice from being a dil to a very difficult mil. She was a very strong opinionated women, wouldn’t be told that her ideas weren’t always right. I learnt to smile and nod, and agree to look into her methods, whether it was cooking, housekeeping, child care, believe me she knew it all !.

If she wants to lay baby on the tummy, just smile and say, he likes to sleep on his back, he sleeps better, it gives him colic is a good one for lots of things. Always back your statement with a smile and the promise to check with midwife, but for now you think you should stick with what you’re doing.

It doesn’t hurt to say she was right about things, or soften it a little, something on the lines of, the midwife said it’s fine to sit him up if he likes, but only for short periods of time, that way you’re both right.
When she says things like, she will protect him from your methods, smile and say, oh he knows we all love him so much.

It’s important to maintain a good relationship with your mil, and remember she’s only trying to help.

So many typos and grammatical errors, time for this Mama to go to sleep!

Thank you everyone so much for being so helpful and willing to give advice! I really appreciate it. God (or whoever/whatever you believe in) bless!

She used to be a lot more confident going out, however she has a health condition that causes her to have seizures. They're started to increased over the past 6 months and although they haven't cased her any physical harm as they aren't conventional seizures, they're embarrassing for her so she doesn't want to go out much anymore.

Things usually come up at random times. When she was cuddling DGB one morning he fell asleep so she put the baby to sleep in the pack-n-play she has for the grandbabies, which was how the stomach sleeping came up. Things usually come up at the dinners, or between DH and her over text. Things not related to me, but between them. She gives him a lot of advice on random things based on him and his siblings and he gets frustrated, like adding cereal to milk so he'll sleep better at night, switching to formula etc.

I've shown her links to studies and she still stands by her belief. I told DH that's fine, we'll just wait until baby can roll from tummy to back to let MIL and FIL have their 'baby day' that they've asked for.

I'm pretty good at just brushing it off since I know it comes from a place of love and concern, I just hope I can help DH with that as well. He can take things very personally. She's just trying to be helpful, and even though this is grandchild #5, she's just as new to this as we are since her relationship with the other 4 weren't the best

Good advice already given, I think you just need to just let it go over your head when she contradicts your parenting, it’s your child to parent your way but to avoid conflicts just ignore what she says and if it’s while you are alone with her don’t even mention it to your husband. He may feel resentment towards her because she is upsetting you.
You don’t mention her age but the older some get the more set in their ways .

Your example of MiL not being aware of (or not accepting) the Back to Sleep rule, shows she’s stuck in the past and not open to new ideas.

You have two options. Either completely ignore her silly remarks and outdated ideas and just carry on sweetly doing things your way or try to educate the women.

For example did you show her literature from organisations like the Lullaby Trust with the statistics showing the amazing decreased in cot deaths since the BtoS campaign was launched?

Also I think you might want to gradually and subtly decrease the amount of time you spend with MiL.

I thought you said you went out to lunches and films together?
Popping in is a kind thing to do and I don’t see how a quick visit could afford the opportunity for the amount of interference you speak of.
Smile and brush off her “advice” when it becomes interference. This is YOUR baby but read some of the other threads on GN to see the consequences of relationships breaking up over intransigence!

I do have other moms and friends I visit, however my MIL asks if I can pop by for an hour here and there (She's unable to leave the house most days now and says seeing the bubs cheers her up) we usually do a 30-60 minute visit for tea, once a month lunch and we have them over for dinner once a week as well. They live a 3 minute walk away so I usually stop in before I head out for the day (at her request)

Do you think she would be hurt or lonely of I started telling her it wasn't a good idea?

I think your husband is right MissKae you seem to spend an inordinate amount of time
with your mother in law. Whilst its good to have this relationship, its also time to stand on your own two feet and make friends with other Mums and younger people.

That meant to say "Advice" in the title. My phone must have corrected it, sorry for the typo!