Ask YC: How do you compensate sweat equity?

I am ready to incorporate but the history is that I've had several technical cofounders who ended up working for 1-3 months and then moving on.

1. How do I compensate these people for their sweat equity fairly?

2. From which pool of stock should I compensate them (they intended on being founders but did not end up being that).

3. How do I also factor in my contribution (design, all funding, and bringing the project to finish with foreign contractors).