Good lawyers are hard to find and you surely need one. If you want to feel out your potential partners ask them if all three of you could meet with a lawyer of their choice (and expense). If they hesitate or refuse or make excuses then walk away and don't look back.

Honest people in this situation will gladly create a fair business ownership plan with a lawyer. It protects everyone involved including the folks you don't know. You need to know if these guys are honest.

Further, take your time to get to know the 2 guys better. Right now what's most important is "Can I work with these guys in the long run?". Business can be like a marriage - you could potentially be spending the majority of your time with these 2 guys if the business is successful and grows rapidly.

Also make sure the other partners can pull their weight. The majority of the company's value will rest on your shoulders (as the developer). So the other partners need to be as active as you are in their own expertise - sales, marketing, support, operations, financing, etc. Don't bring along someone "for the ride", make sure they all work as hard as you do.

So, that's a few thoughts from someone who's gone down this road a few times, for better or worse.

Good luck!