Geo, you are awfully stupid if you don't see the only solution. All the work they did is theirs, if you want to truly own it, then delete all the work they did and finish it yourself. They created all new stuff, and that new stuff is theirs, because, gasp...they created it! Now, stop acting like a damn little kid and handle this is in a professional manner like the grownman-that-shouldn't-be-playing-graal that you are.