I think that while it does seem they are overstepping, it is lots of minor things.
Is this your first child by the way ? I ask, not just because it does sound (just a little) like PFB to me, but also because everyone will be finding their way with what is / isn’t acceptable (you and them). Is this their first grandchild ? They may just be very overexcited. I’ve seen people get strangely territorial over baby’s on threads on here when people are just overexcited, not meaning any harm ( probably) and will calm down. Many older folk also don’t get times and advice has/have changed so to the. It might look like you are going against what they were told was right when they had kids and are trying to help. I think their motives determine how I’d handle this. Why do you think they behave like this ?
You need to speak up for yourself and your child here. Remember you are the parent. For example:
(A) Please give the baby to me to feed now - he is hungry and getting upset.
(B) No, at this time you cannot take the baby on holiday as he is too young to be away from me for extended periods of time. We can discuss again when he’s older if you like, but the answer if no for now.
(C) Do not feed the baby that - it is unhealthy, bad for teeth development and we are limiting his intake. (Although I do think this is a question of degree as an occasional bit of stuff Is ok if you are top of teeth hygiene - daily / several times a day is too much).
Some things I couldn’t get too excited about. The present thing I don’t really get but if you really wanted how about:
(C) I know you were trying to do a nice thing but we were excited about getting the first gifts with our DS face on for people. Please try to think and check with us before you do things like this.
In terms of the walking, I know it’s upsetting not to be present for one of your baby’s firsts but sometimes it happens. We’re they just very excited that they “got” one ? He could have been with your parents or DH and you could have been out of the room when it happened. It is tactless / not nice for them to go on about it but some parents would want to know a milestone happened so they could find out if something triggered it (funny actions for a laugh for example) that they could do to keep trying to get it to happen again. They could have just been really excited about being there for it and not engaging their brain. Again, you could just say:
(D) we were upset to have missed that so while I get you are excited, please can we talk about something else now.
It sounds great your DH is sticking up for you but these are not really earth shattering problems to me and nothing that you shouldn’t / couldn’t deal with yourself at the time it happens with a few firm statements. Your DH can them back you up later if needed. I don’t see this needs to be turned into a major fall out though.
By not asserting yourself it could be they don’t realise your upset. Or do you really think that are they are truly nasty people doing their best to upset you ?
I’d also try to reduce contact a bit (depending on how often you see them - every day perhaps too much, once a month is t too bad to manage them iyswim). Just have lots of groups to go to (or tell them you do and ask they call before dropping in) so you don’t miss them). Keep a coat near the door if needed and just tell them you were headed out if needed. Try:
(E) I’m sorry you’ve come all this way but we’re just headed out to X that can’t be missed. Such a shame - next time be sure to call first so we don’t miss you.
Or
(F) Sorry now is not a good time. We’re just tied up - next time be sure to call first so we have plenty of time to visit.
I guess I’m saying my overall advice is to speak up for yourself / your child when necessary. Good luck.