I don't understand

my sister and brother-in-law. They are away on vacation this week, so my parents stopped by their place to see if everything was okay. Well, it is if you can call it that. They haven't mowed the lawn once yet. They haven't raked leaves from last fall. The inside of the house is a complete disaster. Things are everywhere. You have to watch where you step. It's like an earthquake hit. My sister gave up cleaning a few years ago. We don't talk about it. I guess it's just not part of her routine. She only works 4 days a week and has no children, so it's not that she doesn't have time. My brother-in-law used to help and do things, but he's gotten lax too. I don't understand it. I'm not a neat freak, but I like things to be in their place. It would make me feel terrible to live in a house like that. I think they are both depressed and they can't get out of it because of how they're living. What's going to become of them?

Also, I think my BIL is losing the plot somewhere along the way. His mother died of lung cancer in the fall, so now he has taken up smoking. He says he doesn't care. His father AND mother both died of cancer. Why push it? They'll both be 46 this year.