This is a very difficult situation to deal with - your family member has my sympathy, having seen something similar in my own family.
It is almost impossible toi get people to engage if they don't want or need to do so, so it may be that she has to precipitate something that either he cannot ignore, or that matters are taken out of his hands, which may mean talking to the building society or anybody else where there is a big debt and say I am trying to sort this out but he won't cooperate with me - can you help by taking it a stage further. Drastic, I admit, but maybe he needs a kick where it hurts to get him to engage. A lawyer would be the best, but you said that is not affordable. This is roughly what happened in our family case - he was put in a position where he had no choice but to engage. It wasn't easy or pleasant, in fact it was downright horrible, but it eventually got the job done. In the end we had to force him into individual bankruptcy.