I have no idea about computer coding but...
They could create the option of either TC or gunning. When someone joins the person already in the tank gets to accept as TC or gunner. The TC would drive the tank, sit in the hatch and, like in the real thing, slave the turrent to designated target. The gunner gets motion sickness as they drive around and once target called out, goes to work.
May be a bad idea but something to work with. I did tanks for many a year. The current modeling is fine and all though I would prefer teamwork allowed by two in a vehicle. As an example, firing from defilade requires the TC to keep the maingun slaved roughly on target. Gunner acquires once site picture above the ground, then driver slowly inches forward until tube is above depression and has a clear field of fire. Gunner calls out, vehicle stops, gunner engages, TC determines if they re-engage that target, acquire another or seek different firing position.
It would add the teamwork that took place in WW2 and beyond. It would make Patton proud.
Boo