Why does it matter? They'd have to mutually agree on the shared expenses, and agree on the splitting. If they get a house they both want, and both can afford,

Why does it matter? They'd have to mutually agree on the shared expenses, and agree on the splitting. If they get a house they both want, and both can afford, they split 50/50. Hypothetically, I'm guessing that if whoever made more income wanted a nicer place than the other, they could pay an agreed proportion more (eg, 60/40)