Re: Two teachers...
This is a great thread.
My 'lineage' goes up through Sugano Shihan, but my sensei encourages us to attend courses run by other shihan (for instance, Yamashima, Hiroaki and of course Yamada) whenever they are within travelling range. Of course, that's not quite the same as encouraging us to train at another dojo, but I think openness is the most sensible course if that's what you are planning to do. As other posters have noted, that may also help your teachers understand why you aredoing something a particular way.
The key thing, to my mind, is to steer clear of the "I've been taught a different way: your way is wrong" trap. Just learn from both. After all, if you are in the position of being taught by two teachers, who are you to say that one is wrong and the other is right?
As I say, great thread, very thought-provoking and positive.