UPDATE: So, it's 24 hours before my flght, and I wanted to post an update of my experience.

I did all of this on nwa.com under "manage my reservation"

1.) I was able to move all 3 of my friends to exit row seats.
2.) I was able to move myself to a Coach Choice seat

Aparantly, as long as everyone was on the same PNR as me, I could move more than just 1 companion to an exit row seat.

One thing to note - I could only move 1 person to a Coach Choice seat, and once I did that I would have had to pay $15 for any additional seats in Coach Choice.

So the answer to my question of "For how many companions, as a silver elite, on the same PNR, can you select seats in exit row and coach choice?" is "at least 3 in an exit row, and 1 in coach choice".