Reading the beginning of the saga (and you know it's going to be a whole saga, right?), I wonder if this isn't part of a grieving process. DH and his siblings never had a normal life with MIL. I wonder if he is grieving the loss of any semblance of a normal life. So he just can't let go of the stuff, because it's a mirage. He thinks that if he could just do X, everything will become normal. If he can just keep the right stuff, maybe MIL will change, she will thank him for helping clean out her place, she will suddenly become a better person, etc. etc.