It is absolutely wrong to give them your old app…and is against the honor code of your college. Period.
I agree with @redpoodles …imagine the worst case where the professor finds out it was yours and you get expelled/failed. You think you are being “nice” in helping them cheat but then you get screwed.
“Man, I wish I could but I have horror stories about the academic integrity counsel and I am not getting thrown out of school for this.”
You sound empathetic but are saying NO.
Another reason not to feel guilty is if you give them the app, and they get an A in the class, that is your college giving them the stamp of approval that they know how to create an excellent app. But they really don’t. And if these people get hired and they cannot perform, then employers say “those graduates of University of X don’t know what they are doing” and then they don’t want to hire people like you.
You can say “No but if you tell me your idea I can spend 5 minutes telling you my thoughts on it”
Now for the people in your group ask yourself if you are really letting them do any work?
Sometimes people think they can do it better/faster and just do it themselves.
Are there parts(testing, documentation, presentation) that th eothers can do?