Okay, I'm just starting a new thread because the others are getting too long.
1. Moving into an ally's space... I had and hadn't thought of that. once again I'll say that I don't have a copy of my own special rules right here with me, but I know I don't have anything written about this. How about this: If you move into a territory that an ally is already holding, I will message both you and your ally. If you both agree to allow the second army into the place, the army enters, but gets nothing from the territory. The first person there controls the entire thing... unless he wants to give it up to the other army. If the player that was originally there refuses the other player's access to the territory, the army stays where it came from, and can choose to R+R or recruit.
When moving into an ally's territory, though, it does count as moving, and not as attacking, so you can move farther if you want to.
2. I had thought of that one. I would first randomly choose who gets into the territory first. Then from there, I would say that the second person in is still attacking, but if it is an ally I'd go through the stuff in the previous paragraph. If it was an enemy, I'd choose the defensive orders for the army that got there first (as close to the offensive order they chose to attack the place with), and do the battle between those two armies like that.
3. I'm still not quite decided on that. I think corners are fine, actually. you can move through corners.