I'm glad you're testing them, things are much more fair these days from what I hear custody wise. In dad's day they cared so little about the dad that the court wouldn't even tell him when to show up, they expected the ex wife to tell him and of course she would tell him the wrong day or time so he'd miss it and look like the bad guy. She raised my half brother and sister to just view dad as evil and to treat him as an ATM and as soon as he wouldn't give them money or co sign loans for them anymore (because they never paid and the last attempt my brother was in his freaking 30's) they ghosted him. He's barely met his grandchildren from them and when he did they called him by his first name and gave him the stink eye. I'm done trying with them because all they want to talk to me about is how bad he is, as in looking for dirt from me or if he's leaving them anything (he's not, after like 5 faulted loans they have spent their so called inheritance already). They'd gladly toss me on the street to get the house money but it's basically his only asset and it's in my name because I take care of him now as he's in his 80's and I know I owe him. He's really sad about it if you bring them up but there's no reasoning with them since she brainwashed them at like 5 and 6.

As far as dealing with the ex turning the kids etc, first thing is fight in court and get transcripts. You can show them official records of your fighting for them and as adults that might help. I never saw the cheating myself and I do think he's exaggerated some of it in his mind but I do believe some of it happened and in my mom's case she was always VERY worried about me being around male cousins or sons of her friends, like to the point where a 4 year old notices how stressed mom is about me being in a room with cousin whoever (it wasn't a specific one, any male) and she'd never really ever let me be alone with a younger male relative even ones that were even just a couple of years older than me so as an adult whose been to therapy SA trigger warning I can see that she might have been abused as a child by a family member, it went on SO much back in the day and if young enough, the abuser would be telling the child that the sexual assault is how they show that they love them, and lead her to seek that kind of sexual attention as an adult without knowing why. I think that was why she was the way she was and I can forgive her for that. Dad of course loved her and he's forgiven her too, I mean he cared for her for 10 years with MS, and I've shared this conclusion with him and he agrees. Only one of her sisters is still alive, I'd LOVE to ask her but don't want to ruin her peace at 80 years old.

In your case I will say people who accuse are often either just incredibly insecure due to past trauma or hiding something themselves. In this day and age taking the kids to a family therapist might be a good idea if you can afford to. Or at least getting them some help when they are old enough because they are absorbing all of this and blaming themselves even though as adults we know that's not rational. I personally am comforted by information, so having proof you fought and the DNA might help, plus just letting them know how wanted they are as much as possible.

All you can do is love them and be the best dad to them as possible. Don't engage in the back and forth with them, just model for them love and get some tips from therapists on how to handle not engaging with the drama because from what I've heard that's what kids remember. "Mom said this about Dad but all I ever saw from Dad was how much he loved me and was willing to be there for me, and he never said a bad word about my mom" seems to be the line I hear from well adjusted people coming from divorce. It's hard, but love and actions shines through more than words do. Just keep loving them and try to take it off their plate when they're around you by not engaging. Get someone YOU can vent to afterwards, just never to them. At least not until they are proper grown adults with enough life experience to put it into perspective.