For what it's worth, the newest version of C2 comes with a Turret behavior. I haven't had a chance to check it out, but it may (or may not) be of use to you. Good luck.
If you want to control both tanks, but only one at a time name one 'tank1' and 'tank2' then just have all the code for tank2, or one, disabled until the tank is clicked on. Pretty sure that's possible, but remember to disable the other tak or you'll facepalm...