Carla- ESTJ (could easily seem N, but that's just the organization backing her -- she just follows orders, and Michael plays her like a fiddle).
Simon- Seems ISTP.
Micheal is not only an ISTP, he is the arch-typical ISTP.
No he ain't. Is he impulsive, hot-headed and improvisational like Fi is? Like Jesse is? The primary STP reaction to a hot situation is CHAAAARGE, Michael's always the one in command, the one telling everyone to take a step back and think.
Seriously, look at Season 4, Ep 1. What were Fi and Sam gonna do when he got back? They were gonna charge head-on and shoot it out with the bikers. Michael's reaction? He foresaw that that course of action would result in a few extra holes to breathe out of (Ni), and decided the best course of action was to bluff. Then he came up with an elaborate plan (that did not involve bullets, initially at least) to try and get the poor guy out of trouble -- like he fucking always does. If he's not INTJ, I'm Santa Claus.