It sounds like your oldest is aiming for approval from the one parent he thinks he can get it from.
That isn't on you, it is the place he put himself in with you.
I know when I was younger, and without a lot of resources, drama and approval is all a kid has (until they grow up).
So, I don't think he is going to grow up just yet.
The easy road is hanging with the parent with the much lower expectations of him or that he gets to shine as the 'good' kid in her world.
Unfortunately, it could be a while before you both find some peace, unless, for the 100th time in this situation, you take the much higher road.
As for your daughter, truth is self-evident, she knew the situation at her mom's was wrong, that's why she told you.
Blowback for honesty is another life lesson she will hopefully understand at one point.
You've had to all the heavy lifting, it appears you will have to continue to do so, until the divorce is final.
Actually sounds more like you needed to vent (which is why SI is a good place) and already know you have to have a ways to go before you get some peace.