Those sound like difficult (or as you say, maybe impossible) things to work out. However, I still think this sounds very interesting. Personally, I don't mind seeing ideas that don't work either, in fact getting discussion on them might open up new ideas.
Well, if I can't solve the problems, I'll see what I can do to get something that's psuedo-playable (i.e. more than two rudimentary enemies) before this session ends.
In thinking about it, I think that perhaps the basic idea of splitting up the game play between the two sets of objects-- one group to attack and one ship to dodge-- could be workable and a bit different but that it doesn't work as well in the "defend the friendly units" theme of this session.
At the same time, the game needs _something_-- in a "normal" shmup, because you have to reposition yourself to attack as well as to avoid fire, the player has a reason to move. If you fire automatically from fixed points and just have to dodge fire with the other ship, there's no reason really to put yourself into any danger in the first place. So, like I said, it needs something.
So, I dunno; I'm going to try my best to deliver on the theme and we'll see what I can come up with.