This is weird and it's nonsense. Obviously Leonardo is the captain. First Officer would have to be Raphael, arguing with the captain's decisions then giving in. Donatello IS an engineer, so that's clearly his job. And that only leaves Michaelangelo to be the doctor. ...Don't get too injured, guys.
Agreed, none of them would make a fantastic doctor. I was trying to think of what role Mikey could fill, and honestly I don't think he's grown up enough to be any kind of senior officer. Cowabunga, lower deckers!