So sorry for their loss.
Your daughters in-laws, witlesses or not, are despicable and heartless; I don't think some people realize the emotional devastation that occurs when you lose everything. I know a couple whose house burned down destroying everything, it's been a few years now, but they both still have a massive amount of anxiety and constantly worry about their security. Many too can suffer from a form of post-traumatic stress disorder, so please make sure they (especially the children) get the proper emotional support needed.
You are a doll for taking them in.
Much Love DLL