Not in the same boat, but in the initial beginning, I'd make sure you give them as many opportunities to quit as possible. It'll weed out those who aren't truly dedicated, and may jump ship anyway 3-24 months from now.

I'm not sure how common dropouts are among YC founders, but it's a pattern I've noticed in real life. If something is going to take a long time to accomplish, requiring lots of dedication and persistence, you've got to be 100% certain all parties involved are all-in or they have a high probability of flaking out.