as you said 1 and 2 off.
both engines at a time,then when N1 bellow a certain limit,anticolision light off,so the ground personnel can aproach the plane. (737)
The power is already on APU,air also,so no reason to keep one engine running longer than the other.
If you want to argue with your instructor,just to give him something to think about,you may say that the bridge is on the left side,why not switch off first the nr 1? To avoid damaging the bridge
Just kidding,of course.