He sounds like a "prima dona" - someone who always wants to be catered to and can always find something to complain about. There is no way on this earth that you can be successful pleasing someone like that. Did someone spoil him - put him up on a pedestal - like maybe his mother?

If he is not being respected by his children, it is because he is not commanding that respect. They will never give it just because you keep telling them over and over that they must. He sounds like a childish bully, and the kids are seeing that and getting sick of it.

Having his parents there in the middle of things isn't helping. Mainly, though, it sounds like he is kind of abusive. That probably isn't ever, ever going to change. You might want to think real hard about leaving.

Another issue is the kids. Are you both the biological parents of the same kids? Is he the father of your daughter? If not, that can be a source of trouble too. Eventually, the kids will be gone and you will be alone with him. Do you look forward to that? Sounds to me like you have been trying very hard for a long time.