Yikes, sounds fun.
DS went though something like this and for him it seemed to be about his lack of control. What worked with him was that I gave him 2-3 options rather than telling him what to do directly when I could. So if we were going out instead of telling him to go get ready I started saying things like "do you want to put your shoes on first or your jacket". Meal times I gave him control over parts of it "do you want an apple or banana with breakfast". Bath battle time we used "it's time to get out, do you want Daddy to help you or Mommy".
YMMV but it often worked for us and then at least I was less worn down for the remaining battles
