I agree that living with him is not in your best interest. The de-cluttering will have to go slowly anyway, or you run the risk of further traumatizing him. You cannot live in an environment like that without wanting to clean it up every minute of every day and that will put a strain on your relationship with him. My best advice is to plan a day a every couple weeks to help him, but limit it to that. It didn't get full overnight, and it won't get emptied that quickly either. He needs to address his hoarding through therapy or he will most likely keep acquiring "stuff". It sounds like he is holding onto a lot of her items and I am wondering if he doesn't need some grief counseling as well to help deal with her loss. You need to get some professionals involved to make sure he is handled the approprate way. You are a great sister or you wouldn't be doing all this, so just do it right so you don't destroy your relationship with hime.