Ask them to assess when they think the startup will be profitable, considering everything invested to date, then reproportion your equity accordingly. So if eac

Ask them to assess when they think the startup will be profitable, considering everything invested to date, then reproportion your equity accordingly. So if each of you have 25%, the consensus is 2 years to profitability, and you spent 2 years there already, then you should agree to reduce your share to 12.5%, splitting the other 12.5% between the remaining 3 founders. You can also offer to play an advisory role for a bit more.