Hi Ivy, sorry to see you are having to deal with all this.
The relationship with In-Laws is greatly tested after Dday. Very few in-laws will rally round the BS but it can happen for the lucky few. They will probably go into denial and rugsweep, find every reason to lay blame your way. It is just one more relationship that gets battered thanks to the WS's behavior. I have spent the last 3 years in total bewilderment over my MILs silence and inability to recognize what her son has done. Sadly she passed away last month so now it is futile to even wonder what she really thought.
Try not to lay blame their way, they are probably mortified but just don't have the tools to deal with it. Just concentrate on looking after YOURSELF and giving your energies to that. Don't waste time wondering what they think, what they are doing or saying. You will just end up emotionally and physically exhausted and you have enough work on your hands.
Give yourself a hug today and realize that everything you are feeling right now, the anger, the hurt, the confusion - is all normal. It is living process but you will work through it.
Keep posting here and taking care of yourself.
Hugs to you.