Having read all your posts I think their are a few issues. You are clearly trying to ensure there is good and reasonable contact between your DS and his grandparents. They want more and are trying to force it on you. This has caused the anger you feel at their previous manipulation to bubble over. Stand your ground re childcare, but maybe reduce it by one day and let them have him. Kids are pretty resilient, and one afternoon of not following your rules to the letter won't hurt him.
The other issue is harder. You need DH on your side. However, he obviously loves his family and is worried about his mum. His mother's health will effect the way he sees things. You need to resolve the feelings around the house, and he needs to understand how threatened and manipulated you feel by his family. It's important you end up on the same page.
Thirdly, you need to chill. You come across, possibly wrongly, if so I am sorry, as very uptight and controlling. Try to relax a little. Children benefit from different influences. If you try and completely control your sons experiences you will do yourself and him no good. I am talking in general here.