My sister’s ex is dragging their kids into adult drama and I feel helpless watching it

The title really says it all. My sister is going through a really nasty separation/divorce right now. Her ex is a narcissist and was extremely emotionally abusive throughout their relationship.

They have two kids together (6 and 8), and I’ve basically become a second mom to them because they spend so much time with me. Their dad (I’ll call him Boris) never really had much to do with them when they were younger and would constantly pick on them. to the point where they’d be crying and he’d mock them for it (calling them inappropriate names that I can't repeat here) instead of comforting them, saying it ‘builds character'… when they were literally 3 and 5.

Since the day they were born, my mom and I have always helped my sister whenever she needed it. That’s only increased since she and Boris separated about a year and a half ago. She had to go back to work after being off for almost 6 years, and now she’s basically supporting the kids on her own because he’s withholding child support.

My mom and I have stepped up a lot — emotionally, physically, and financially. And honestly, it’s not something either of us can really afford, but we make it work because those kids come first.

Both boys have been struggling with the separation. We’ve always suspected he’s been saying inappropriate things to them, but now we actually have proof. He’s told them their mom is lying about why they don’t see him more (which he admitted to in writing), and he also told them he doesn’t like my mom because “she’s mean to him.” This man is 40 years old.

He keeps pulling them into the conflict, and I’m sure there’s more being said that we don’t even know about. He’s even got my older nephew lying for him about things.

I’m honestly really struggling with how to deal with all of this. The kids are with my mom and me 2–3 times a week. I take them to and from school, bring them to activities, help take care of them day-to-day. Between working two jobs and helping with the boys, I basically have no social life anymore.

I’m not complaining — I would do anything for those kids — but it’s really hard watching him try to undermine their relationships with us, and feeling like there’s not much I can actually do about it.

Thank you for taking the time to read this. I really appreciate it.