Sit down with the kids and together you all can pack his things up for him to get out of the house. I bet with all they have been through they would love that closure and it will bring them closer to you.
My AW tried to tell me I was the reason she had an affair with my bf for 6 months. Things were crappy for us back then and I can see how it happened once. I told her it was BS how long it happened and through some very good times.
They will always point the finger away from themselves. It's too painful to point at themselves and lay blame where it belongs.