Sammy, I understand how sucky it is.

When we had DD we had these issues and my advice to you and DH is to sit down and talk about how you feel about this as an issue as a whole - not nit picky things (cos it's very easy to do) but about the undermining as parents. Then either you together or just DH need to tell them 'hey, look I know you don't mean to do it, but we're feeling really xxxxx (insert your own feelings here) about some of the comments you make toawrds us. We realise that you are experienced parents but we are parenting our children the way we chose. We are doing this consciously and we'd really appreciate some support.'

I know how hard this may seem, but from experience this kind of external conflict can put strain in all sorts of places.
You guys are a team. A good team. One who knows the best for their smallest members - no questions.
Don't worry about making people 'feel bad'. You are already feeling bad and whether consciously or not they have brought this about.

FWIW when my DD was 6 weeks old, my ILs took DH aside (cos they are scared of me) and gave him a list of all the things we 'should' be doing - leaving DD with them one day a week, not breastfeeding as she was under nourished, giving her solids, letting go of the apron strings etc - and no I'm not joking. They just assumed DH would take it on board I think but of course he backed me up and we made it clear that while we appreciated they wanted to 'help' that when we needed it we would ask.
I'm glad we did that as it nipped it right in the bub instead of it festering for a couple of years.

My parents also have their views on the way children should be raised and i am certainly very vocal in my opinions towards them when the need arises. I appreciate it's their house and their rules and all, but they are my children and my rules are of the ultimate importance to them wherever they are.

Whether they agree with my opinions or think highly of my parenting or not, while I would be sad, I'd rather be confident in my parenting choices, than feel forced into something.

big again babe.
I think you're doing a great job. And I would have done/felt everything you did too.