Cecili, lots of good advice here already. At the risk of stating the obvious, it is a similar set of questions, but different expectations (from both sides) if you are joining the team for equity only VS being paid a market-rate salary. The expectations can/should also be tempered if the two founders have substantially greater relevant business experience. If part or most of your compensation will be equity then your primary objective needs to be to vet the viability of the business as well as the track record of the founders to execute - no different than any other investor:
1. what is the size of the addressable market?
2. do they have 'traction'? if so how did they get it? if not what is their DETAILED plan to get it?
3. What is the target market - SMB, enterprise, consumers?
4. What is the ideal prospect: i.e. "VP of marketing for retail grocery chains with 10-30 locations" - don't just settle for "small to medium sized businesses" or "consumers".
5. what is the DETAILED plan to reach these prospects in terms of marketing, business development, sales, distribution..?
6. Does the business require external funding to survive? is yes, then how will we get it?
7. What is the relevant market experience that the founders bring to the table? I see that you are a recent college grad so if the other members have significant relevant market experience, how do you compensate for your lack of experience? If all 3 of you are relatively inexperienced then what is the plan to obtain market knowledge? i.e. advisors, investors, ???
8. Is there any defensible IP?
9. what does competition look like? how do we compete? and what have you done to collect intelligence on the competition?
10. I would ask to spend some time as a team reviewing their detailed operating budget - hopefully they have a detailed spreadsheet that shows who the prospects are, what the budgeted line-items are to reach the prospects, what those marketing/business development/sales costs are, support costs, personnel plan, tech budget, etc. If these guys have been at this for 2 years and they've been through 2 incubators then you should expect some very detailed plans - if they don't yet have a product then they had better have some really solid plans. The founders should be able to walk through the plans with you and connect all the dots and it should make sense to you. There should be no "and here a miracle happens" spots in the plan. To go into this level of detail it would be reasonable for them to request that you sing an NDA. If they don't ask then it would be reasonable for you to raise a small yellow flag of caution.