They're pushing for adoption

Me and my husband are fostering a brother and a sister. They were removed for the mom's boyfriend molesting the sister. The mom has been having regular visits and court dates so we figured they would go back but today in front of the kids the mom asked are we open to adoption. I asked why if her rights aren't terminated and their worker said it's going that way. I asked why and they said mom lied about cutting off contact with the boyfriend and actually married him and he's been living in her home. When they spoke to her on it she got upset and said she's not gonna leave him and she should be able to have her love life and kids. The mom has made it clear she's not leaving him. My foster said asked if he could go live with his mom since the boyfriend never touched him and the worker of course said no. And he got angry and was screaming that it's not fear which caused his sister to get emotional and go outside. This was of course an extremely hard conversation and it's sad that mom has put in the work but won't do the one thing that's keeping her kids out of her custody. I really don't know how to offer them the best comfort.