In situations like this I KNOW you can't just throw everything away but neither can you let things as they are go on. You something nuanced and different to each hoarder, but it will involves some therapy, getting rid of stuff and keeping stuff.
It reminds me of an idea that you can(or should be able) to trust your family enough to argue with them and have both come out on the other side still loving each other.
Tldr: You trust your family enough to argue with them.