Sure, that's easy enough to do. You need to use the driver, gunner, and commander commands.
Let's say you have a tank named tank1, where your 3 crewmembers currently are. Let's say you want to move them into an empty tank, tank2. Your script or activation field would have the following code:
driver tank1 moveInDriver tank2
gunner tank1 moveInGunner tank2
commander tank1 moveInCommander tank2
I'm not sure, but you may or may not also have to use the assignAs... commands.