Back access is good.  My oven has a handle on the top so you move the oven for a second to turn the pan and then put it back.

If you're in a BWCA situation, two ovens won't help because there generally is only one spot a reflector oven can sit in front of the fire grate.  Perhaps in Quetico you could get two to work, but again it depends on the configuration of the fire pit.  Most I have seen are closed on three sides.

As far as volume, it depends on the oven.  Mine holds a 9" round pan.  You can make 9 smaller biscuits or 9 smaller brownies.  For that many people it would be good for only a tiny supplement to the meal. I usually cook for 4 and it is plenty big for that many.

I have however seen reflector ovens that hold a 13" x 9" rectangular bake pan.  That holds quite a bit more.  Is it enough for 9 people?  I don't know.  I guess you have to answer that.