Major Family Problems

Hey all. I am having some really bad family problems right now. It really sucks. But what happened is, my step-dad's parents stay with us january thru march every year right? Well this year, my grandpa developed a habit of touching mine and my moms butt and boobs. I truly thought it might have been an accident by the way it was done and plus, he's on so much medication that sometimes he dont even remember my name. And on top of that, he's got signs of dimensia. But I told my mom about these times when they happened, and she said it had happened to her too. And so she asked my stepdad to talk to him about it. 3 times. But the fat b***ard never did until it happened again friday. Cuz he did it twice in less than a minute and there was no way it could have been an accident. Then he lied sayin I was bent over and I know for a fact I wasn't because I can't bend over!!!! But it started a lot of caca with my family. My grandma came in and basically called my mom a liar to her face and disrespected her majorly in her own home!!! I mean, she's never liked my mom but this was way out of line. But thing is, they left and are staying somewhere else until they go home. Well, my stepdad and brother have been visiting with them, and no one really told my little brother what happened exactly. Now that b*tch is feeding him full of sh*t and lies. She totally turned the story around. And I think she is pressing my step dad to divorce my mom, (they were already on the verge of it anyways) and last night I got up and they were arguing in the garage....I mean really loud. I really think they are going to. I know my mom would be better off without him, but I don't want her to work 2 and 3 jobs like she used too. No one should have to do that. And sometimes I feel like it's my fault, because a bug part of the reason he wants a divorce is because of josh....He doesn't want a baby in the house and he doesn't want to listen to him cry.......But oh well. He shouldn't be such a heartless selfish a**hole. And I told my mom I was sorry for causing all of it and she told me don't be because it wasn't my fault. She told me i'm more important than my stepdad is because she's loved me longer and i'm gonna be hers forever guaranteed. He won't. I just feel really bad, I don't want her to have to go through this....She is seriously on the edge of a nervous break down. And just to add to it, my little brother told my stepdad that he wanted to go with him if they divorce because he doesnt want to see my mom every day. I swear to god I f***ing back handed him for that. I don't even like the kid and really don't want him to live with me but it about broke my moms heart when my stepdad told her what he said......Like he was rubbing her face in it. I dunno.....I am really confused.....I know she'd be better off emotionally with a divorce, but she's had it easy the past few years because he brings in the money and she only had to get a job cuz she's helping with josh and my step dad refuses to. So I really don't know. Part of me wants them too, part of me doesn't. What do you think? Sorry I made this so long. I just needed to vent. I am really stressed right now.