I would nope the hell out of there.
1) You are not convinced the idea is disruptive/feasible enough
2) They want YOU to do all the work, yet only give you 1/3rd equity. What do they have to bring to the table? Probably nothing.
3) You don't need them. Ask yourself: would I build this if I would get 100% equity? Since you also have plans of your own, the answer would most probably be no.