This sounds like compulsive hoarding. It is one of the variants of
OCDObsessive-compulsive disorder. It is a tough one. There are a few specialized programs that will send people out to the home and do a combination of therapy and help to sort and throw things out.
Saving other people from themselves is always a challenge if they do not see it as a problem. The likelihood that they are reinforcing each other's behavior increases the challenge.
Look for an 'opening wedge' where they have trouble with some part of the behavior, the cost, trouble cleaning, whatever. Without that you have no hope.
Realize that it is probably a way to make a dangerous world feel safer. Listen carefully for the underlying anxieties and see if you can address them subtly without reference to the hoarding.