I like that they're 100% invested in it, all living together and pooling income and paying off debt, but at the same time they're not owning anything long-term together. They get all the best parts of interdependence with very few of the downsides.
Waaay better than something like buying a duplex with a sibling, where you're not all that linked in terms of support or daily interactions, but you're horribly bound to the anchor of the shared building ownership.