OP I honestly am sitting open mouthed with shock reading your posts, because I didn't think anyone else had to go through what I have been living with for the past few years. Your inlaws sound identical to mine in every way (apart from asking to have an abortion).
The control, treating my DH like an imbicile to be controlled, his confusion hurt and surrender to it all, the excessive gift buying for DCs, wanting to dress my DH and our kids, wanting to buy their full winter and summer wardrobe, questioning every decision we make, wanting to spend every weekend and holiday with us. They wanted the DCs to themselves without us every Sunday. There were constant arguements if we wanted to spend even one weekend by ourselves. I could go on..
OP the only solution is boundaries. The problem with that though is that people like this will never, and I mean never, respect your boundaries. The only way to set boundaries with manipulative control freaks, in my experience, is to put a huge geographical distance between you. We emigrated to Australia.
We didn't move to Australia because of them, but the move in itself which was for other reasons obviously improved a lot of our problems.
We have peace, freedom, we feel like grown ups living our own lives. We have our issues like most people but we have the freedom to fuck up and learn and grow and make better decisions.
If you think they are bad now, wait until you try to get away, then you will see the full extent of the manipulation. We've been told we have caused nothing but heartache, loneliness, stress, we've contributed to their heart problems, fibromyalgia, ulcers. I'm surprised they don't blame us for their dandruff.
My parents on the other hand, while they were incredibly sad to see us go, wished us well with nothing but support and love and encouragement.
I'm getting great benefit from the other replies too. I haven't got it all worked out. There are still control issues. My DH and I still argue over it all. I find myself in knots of resentment towards them over how they treat my DH and I find myself in knots of resentment towards him for not handling them better. I hate that they still 'control' my feelings in this way. I know I need to let go of this resentment but I don't know how. I start psychotherapy this week, I can't do it by myself.
OP you sound incredibly mature for your age. Best wishes.