OP I'm so sorry that your family is going through this, and sorry for all that you have lost and how much your world has changed. It sounds like you are all already going through so much with SD, to have something like this happen as well would just be too much to handle.
I'm glad that you'll be getting family counseling. Hopefully it will help you all to deal with the fallout, something like this affects so many aspects of your life.
My family went through something similar when I was a young child. My parents did a great job of shielding us from it, it wasn't until I was an adult that it was fully explained to me. My grandmother stayed with my grandfather for many more years, until he died. For her, she stayed because he was a violently abusive man and threatened to kill her if she left. She was just so beaten down that she never found the strength to leave. I think you need to know more about why your MIL has stayed... Maybe she's afraid, maybe she's in denial, maybe FIL is a very persuasive & convincing man and has convinced her that what he did wasn't so bad... None of these reasons really excuse her staying and supporting him and covering it up. But they may go some way towards explaining it. I think you need to know just so you can make decisions on whether to continue to allow her in your lives.
Sending hugs and strength to you & your family.
Sent from my GT-I9195T using The Bub Hub mobile app