As a gp, I often host meals for my dd's, their partners and my gc's. They all have different likes and dislikes, but I will not arrange meals around this because it would be impossible and I don't run a restaurant. I never get complaints because I don't give them opportunity but neither do I ridicule their likes and dislikes. I tell them what it is, but they all unfailingly turn up.
To be honest op, I think the food situation is getting in the way of the support you wanted with regard to your PIL's intolerance of your dcs. This is because they are stuck in their ways and want to protect their property. Sad but true.
Two of my gc's live with me and I tend to buy furniture etc around them - recent ebay sofa and second hand leather sofa and chair from a family member. They don't have to do this though, do they? I think they will settle/calm down in a day or two if you are still there. As you get older, you do get a bit more intolerant.
I would have gone to the park with you whether I wanted to or not. Its about making you welcome and I think they made a mistake there which has soured the start of your break.
As for the meal, well I would not be happy with you at all. I am pathetically grateful if I get a meal cooked for me. Memories here of my nan's casserole and rice pudding which I ate with a death stare from my dad. You should have encouraged your ds to show a willing as they would have seen the difficulties you face.
Your inlaws sound selfish and intolerant, but you sadly have not come across too well and aibu is always a bear pit. Just hope you don't feel even worse now on your break.