I want to respect their father, and his beliefs.
Why? Do either your children's father or his beliefs respect you? Clearly they don't respect you! And guess what... he and his belief system are going to poison your children's minds against you, and teach them to disrespect you as well.
So you made a "vow"... BIG DEAL. He made one too. The second - the very instant he started disrespecting you - he broke that vow. Because you don't disrespect someone you LOVE; someone you HONOUR; someone you CHERISH. His disrespect and contempt toward you releases you from your "vow". Don't let anyone send you on a guilt trip over the "vow" - you did your best, but did he? Or were you the one making nice when he was being an ass? Or covering his ass, or making excuses for him when he "forgot" stuff or behaved badly? Or putting on your very best Kingdom Smile™ at the Meetings™ when the two of you had an argument in the car on your way there?
The thing about the kind of payback you're proposing is that it only validates all the bullshit the WTS says about Apostates™ and solidifies the average dumbed-down JW's perception that you are the ENEMY. I agree that revenge fantasies can be absolutely delicious, but don't waste your time creating drama for these people - they aren't worth the energy. You need your energy for getting your kids out of that stupid cult, and getting custody away from your loser ex-husband, and starting a wonderful, successful JW-free life of your own. Don't let them get to you, because your future is going to be so much better without them. When you look back at your JW life 20 years from now, you are going to be light-years ahead of them while they will all still be stagnating in the cesspool-of-the-mind that is the JW belief system. Who cares if the Elders™ know it's crap - they're stupid enough to stay in it - do you know why??? Because outside of the JWs they will never amount to anything - and the WTS has them believing that if they Wait On Jehovah™ they'll be PRINCES among men. They are the big fish in the small pond - they'd never survive outside of it. Don't give them a second thought - they are of such little consequence in the big picture of your life - they only have those Privileges™ because they were born with a penis. BIG DEAL, right?