For all its benefits, the conventional wisdom of HN that one should pay off their mortgage prior to a startup may often be a mistake. A mortgage is leverage, and the cash used to pay ahead twenty years would be better used for a longer runway - $100,000 will cover many months of mortgage payments. What would most startups do for $100,000 worth of seed money?
Likewise, if a family keeps someone from going all-in to the startup that's only an issue when the other founders believe that going all in is a point of pride. In this case however, it's not that your cofounder wasn't going all in, it was that he wasn't even anteing up.
The rest of the time is spent on working for your startup. When I was co-owner of a isv our main income in the beginning was consultancy for clients. In addition we developed our product and used the spare money to hire additional developers. The consultancy work made sure we had a minimal paycheck at the end of the month which would pay our mortage and the bills.
Maybe this model is not sustainable anymore with being quick to the market and bead competitors on speed. But it worked in that period of time.