Trouble with my mothers new lifestyle, how to help?

[Spring]

I am 22 yrs old and moved out of my parents home. Last year my mother had an affair on my father after they had been married 22 + years. She had an affair with a women. My mother is now dating this women and has been since the affair. Her and my dad worked a deal where they have the house and an apartment, they rotate who gets the house every other week since I have a younger bro and sis living at the house and they both want to be involved in their lives equally. But my mother has been wanting to skip her week with my siblings and stay at the apartment with her girlfriend. Also my brother age 13 is having a hard time dealing with this but my mom will not acknowledge this. we all have tried talking to her and praying for her but nothing changes. She thinks my brother is being awful to her but he feels angry with how our family has changed, hes having trouble coping and he blames her, since she cheated and is now a lesbian. What can I do to help? My mom will not listen to me and my dad is feeling like my mom and my brother relationship is not his concern. Please help.