The only thing I see that would need to be incorporated, is some sort of a run switch, where by if one xfer switch starts it, the other start circuit is locked out, Xfer is still enabled, but the start sequence is interupted. Depending on the internal engineering of the xfer switch, that may already be accomplished.
You might want to look at total start load to make sure that if both tried to come online at the same time, you wouldn't overload the generator, a timer circuit on one would sove that. It means that if it(the one with the timer) came on first, the timer would have to time out before it would xfer, a few seconds at most.
It's not hard to glum out. Just takes a little thinking.