[jjmiv]

work with a lawyer. it seems like you need to do this anyway to stabilize the next phase of your business.

you need to put a buyout in writing with an end date (yes, with lawyers help). that way if they actually come out of their shack to cash in when you reach better growth you can point to this legal document.

i would consider to put everything in writing- your work and effort, start to omit their info from the website and products, but i would not remove their name + cofounder from things until you've issued that document with an end date and timeline of how you will terminate them from your business.