Startup with three founders

For point number 1. you can sign co founder agreement which define your role, responsibility and other factors like shareholding for initial stage.
for point no. 2 you need to register your company as Pvt ltd for no later stage when investor like to take exit through or as mutually decided . 99% investor invest in any company in exchange of equity to get funding you have to have company and split the pie among co founders and investors.

if need any more clarification please write us or ipforstartup@icloud.com hola@ipforstartup.com