That's a really complicated subject that lots of developers get stuck with sooner or later.
Most commercial Titles 'cheat' when it comes to that. Ever Bot is passable with the other Bots, but they make sure that you never actually witness a Bot actually walking through another one. Of a collision is detected, the other bot will have a 'stepping out of the way' animation and move a little to preserve the illusion of intelligence. Also, a nice collision avoidance will help things as well, since no Bot will actually walk towards another one in the first place.
So the best thing to do is keep a nice collision avoidance system for all your bots and in the unlikely(but possible) event that to Bots get stuck, you set them passable with each other to avoid FPS drops and other nasty things like that. I know for sure that the game "The Thing" followed the exact same procedure, and I'm sure many others did too.
I'll let you guys know how my collision avoidance goes on. I don't like to 'cheat' in any way so I'll only do the passable thing if everything else fails or doesn't work as expected.
