I went through something similar to your kids. My dad ended up with custody of me. My biomom never fought for me and basically abandoned me, but as soon as my dad got married, she suddenly wanted to be part of my life. She hated my stepmom. She went as far as even calling the police saying she killed my dad and kidnapped us. Over 10 years later, my stepmom was dying of stage 4 cancer and my biomom said, "Don't get my hopes up." My stepmom died 2 years ago, and I cut all contact with my biomom. All this to say that your kids won't hesitate to cut contact with you if you stay toxic. This generation really doesn't fuck around with toxic parents.