What is best practice for mounting and interacting with vehicles?

I have plans to include several vehicles in my 3D shooter. In a couple of the vehicles, I want one player to drive and another to shoot the main gun (turret gun in the tank, chain gun on a jeep, etc.)

I have one player possess the vehicle and drive it, that works now. But I am not sure how to have a second player possess the vehicle’s gun since the vehicle in its entirety is a single pawn.

Or should I not possess the vehicle at all, but simply control the vehicle’s features based upon the seat a player is occupying?

What is the best practice for something like mounting and interacting with a vehicle that has seats for more than one player?