Wait a minute, aren't you the guy who gives them 5 minutes to accept once you make your offer?
If they did their interviews/acceptance AFTER you, it would be the same situation with YOU pressuring founders before they'd heard back from anyone else!
Pot. Kettle. If you really care about the founders then you all need to get your schedules together so founders have the option of choosing from multiple offers. Leave the window open longer. It's pretty easy. Give them the forms and have them mail them back once they decide. Like college acceptance; this is a solved problem.