This is a long one... please help me.?

ok so this started years ago, this is between my husband, his brother, his sister, his mother, all their spouses, and affects all the children.. 11 total... here goes. my mother in law has had a boyfriend for the last 13 years or so and hes the bottom of the pit lowest of the low. everyone in this family has awful stories about him and most of us want him gone so here's the dilemma, in 2006 he left my mother in law and moved in with another woman same night, then my MIL tried to kill herself to win him back. when that didn't work she went into a deep depression and wouldn't eat or even move, now all of her children and their spouses got together to try to talk some sense into her explaining how we all felt and what he had done to everyone. well he showed me his 2 times, he showed my sister in law his and then tried to enter her room. he drilled a hole in the restroom walls to sneak peeks at everyone while we showered, and was caught. now this doest even scratch the surface but the largest blows were when my sister in law told all of us that he touched her , and then she caught him with her daughter on his lap in what looked unsettling to her... now my mother in law knows all of this but it doesn't seem to bother her, well my husband and myself told her that we wouldn't go around her and that she couldn't see her grandchildren if she didn't end this Madness, she chose him.. ok well then we talked to my brother in law and my sister in law for support and my sister in law was so scared of her mother that she chose him as well.. my brother in law is on the same page with us about not being around this man but they wont let go of their mother, so now myself and my husband are left in the cold, that part doest bother me except my six year old is starting to ask questions and seems angry... our kids all go to the same school and my sister in law and i cant stand to be in the same room... what can i do