Who said you could move the crew around? <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> They stay put when the rig is moved. How they actually get there with the sail in the way is not part of the theoretical argument. (If you change more than one variable, then it's impossible to discuss the effect of just moving the rig. Start with the crew in the middle if you like - the net effect will be the same).

Righting moment is a torque. The total bouyancy and total weight forces are always equal. What changes is the moment arm. It makes no sense to talk about just bouyancy providing righting moment.

Capsize moment is also a torque (sail pressure one way up high, dagger pressure the other way down low).

The way to look at this is one torque countering the other torque. It makes little difference whether the force from the sail is left or right of the combined CG.

Force diagrams of the sort I provided are a standard way of showing these things. English sometimes falls short.