First, My using English is not good. Thanks.

In the Vehicle.

指揮官's席へ (move to Commander's Seat) and 砲手's席へ (move to Gunner's Seat)
No need a ''s' and This is need the 'move' word. like a '移る' or '移動' for end of the word. I think '指揮官席へ移る' or '指揮官席へ移動' and '砲手席へ移る' or '砲手席へ移動' are more suitable.

助手席へ (move to Passenger Seat)
The '助手' is meaning the Assistant in English. I think '後部' or '乗客' are more suitable. Also This is need a 'move' word.
Like a '後部席へ移る' or '乗客席へ移動'.

外側にターン/内側にターン (Turn Ourt / Trun in)
Many Japanese will think for Turn of the Car. This will lead to confusion. '顔を出す (Turn Out)' and '中に入る' (Turn In) are more suitable. The '顔を出す' mean 'I put out face to outside from the Car' in English.
the '中に入る' mean is 'Retract the face to the car' in English.