I have a complicated situation.....

Long story short we just found out a year ago my mom was raped and abused by my grandfather (he does not know we know) not her real dad but the man that raised her and has been my grandpa all my life..

I have always loved them but obviously now I can't stand my grandpa I have no desire to ever see him again. Problem is they come as a team my grandma is extremely naive and protective of him. We aren't sure how much she really knows that happened. She's extremely sensitive. She is genuine and truly loves us. But we all question what type of mom she was to let this stuff go on..

I live away from home so family comes to visit and stays a week or so. My mom has made it clear she has cut them off from comunication... she would love to mend the relationship with her mom but just KNOWS that her mom would choose him over her, basically be naive to it and lie to herself becuase she's not strong enough to leave my grandpa. So my mom has decided to just not even try becuase it will only cause so much hurt and send my grandma downward and probably make the whole thing more of a mess it already is. I'm not sure what they think or know as why my mom doesn't talk to them but they just completely ignore it (don't bring her up around me anymore) 

So that puts me in the worst situation, becuase if I say something or block them out my life.. it's obvious something's wrong and will open up the can of worms that my mom doesn't want to open. I have a four year old daughter and 4 mo th son... they are here now and have visited a couple times.. and I feel so angry SO angry I have to deal with this is my own house, I have to continually makes sure my daughter is not with him alone, I have to deal with him sitting in my home eating my food, hanging out together like everything is ok and it's freaking NOT. I don't know if I can take this. It may seem obvious to you on the outside to just block them out my life, but idk it's just complicated it would completely devastate my grandma and while I don't think she's the best mom I think she's just naive to it all. It would hurt me to see her hurt. She would probably never recover or know how to move on by herself. So it's like just to keep the peace I have to endure this man in my house. It seems insane I know and I can't believe any of this is even true. My mom has multiple personalities from this and it has basically ruined her entire life. All her memories of getting married and raising kids ahave been stolen from her. Anyways.... if you truly loved your grandma like picture the grandma you love now, and didn't want to break her... what would you do in this situation? I feel like I have every right to say your not aloud in my home, and not deal with this but equally I cant break my grandma and I have to respect what my mom wants.....for them to just remain the way the are naive to it all. If I block them out my life, it would cause everything to blow up. 

I'm about to lose my shit on this guy I can't stand this. I can't stand him here.