First step - pick one.
If you think its going to fail and your partners are just wasting their time. Sign it all over them. Assign them the IP and walk away.
If on the other hand you think that while your involvement has come to an end - that they still have a chance then sit down with them. Get it setup in a form where you can have equity and agree what share of that equity you will have - but it sounds from the agreement you already have you have 25%. Sign over the IP to this entity (they won't be able to sell it or do anything if you don't do this - and you want to give them a fighting chance). If you still want to be an advisor or they do - then that is your choice. The net result of all this is that you will be a shareholder with your investment being the work that you did.
A Note on amount of equity: You have put two years work in at the riskiest part of the game (at the very start when everything is unknown). They might want to argue you down a bit because it's still very high risk - and that would probably be fair - but I would say that's their call if they want to go down that road. Ask yourself if they would have any chance going forward without those 2 years work.