I'm so sorry to hear about your dad, dubstepped. I was with both my parents when they entered hospice, my mom in 2007 and my dad in 2010. Certain family members decided on their own to start shunning me (to varying degrees) after my mom passed. They didn't interfere with my spending the nights in dad's room (so he'd never be alone) and we had normal conversations about his condition and planning for how to handle things afterward. However, when it came to his memorial service, I was warned not to show up at the gathering afterwards for the "friends" or there would be a scene. I decided to let them wallow in their piety and self-righteousness in peace.
I'm very glad your mom is clearing the path for you to spend some time with your dad. That's very classy of her. I hope you can maintain a close relationship with her after this is over. She's gonna need you, whether she realizes it or not.
Stay strong, my friend.