Starting to feel like the only patch of grass at the dog park yet? You haven't had an easy months friend :-(
Funerals are traumatic and when you throw in the level of dysfunction in his family it is a recipe for lots of drama. I can totally see you not wanting to file for separation while that's going on.
Hopefully you can stay a bit detached from the sibling arguments that may arise and remember that our tendency to want to fix things that are not our problem really is NOT our problem. I'm assuming the kids will be going? Might want to think about having a plan to keep them away from the fray like suggesting you guys stay at a hotel instead of at mil's where you can't escape?
Deep breaths, find something good to read and let him deal with his siblings. There are some beautiful areas around DC to take kiddo to if its depressing and the sibs are at each others throat running around to claim possessions and such.
Sorry my friend, I'd puppysit if you lived around here - nothing like a puppy to make you forget the stress.
Hang in there - take care of you and DS. Hopefully AH will turn to you and not ON you through this but keep in mind that he's not allowed to take it out on you.