Hmm, I see. That's sound cool, I thought I can have only one tank on me at a time, so I did not even tried to have more. :D
I have seen a game with a similar idea with weapons, and it was a lot of fun, so that could work.
In that case, I would adjust the tanks position from a fix distance from your character, so they would make a ring around.
And maybe you could use them as shields too. :D