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.

I have spent the last 20 years living with a hoarder and my advice to you is Do Not move into his house.
Help him but do it from the safety & sanity of your own home.
He really does need therapy to over come this problem.
There are some very good books you should read.
"Buried In Treasures" and "Digging Out" are just two of them.
Good luck and best wishes.
Sincerely, Tillie

My sympathies to you, you've begun a very difficult task--tackling the house and dealing with your brother's hoarding illness. It takes psych. treatment to keep him from continuing this pattern. I think you're going to get extremely frustrated trying to do this on your own with him. Do you have any other family or friends that can lend a hand? You're going about it the right way, a space at a time. Good luck to you, I wish I had more advice for you (and me).