My mom had an incestuous relationship with my sister

My mom has been having an incestuous relationship with my sister. I had assumed that they were just extremely close up until they moved in with us, but actually they were having sex. Both my sister and my mom were justifiably angry at my dad for leaving my mom because of her affair with my sister. I am the only one who knows what has been going on because my dad won't listen to me. Now he is having a relationship with his sister and doesn't care what I think at all. My sister and my mom are in counseling so hopefully they can work through it. Maybe my dad and his sister will go into couples counseling as well. I just wish that I could bring my family back together again.