I've also done overlapping batches, which is hairy enough - but manageable. 1 mash, lauter into the first BK, then another mash while the first is coming to a boil, lauter into the second pot, chill the first while boiling the second. I don't think I could manage 2 simultaneous mashes. Hops can be measured out and marked ahead of time, so mixing up which hops in which batch shouldn't be a problem if you're organized. If you're comfortable with your process, go for it man! More beer in less time = better.