It sounds like you should just quit the company and take the codebase with you. It might seem like it sucks because they got some money out of it but you 100% do not want to work with these guys.
They very likely have the failure bound mindset of "ideas are the most important thing, I'll just hire a guy off craigslist to write the code".
My prediction is if you quit they'll think "so what" and try to hire some random engineer without understanding what they'd have to do then burn through the money and fade away (or just keep the money and do nothing).
I don't know what contracts you signed but make sure you check that first (and talk to a lawyer).
Also sounds like one of these scummy incubators that charge mentor fees and the like (basically tax evasion schemes). 4 founders seems like a lot if there's just one engineer.