Many colleges rent equipment in their rec department. REI and few other outdoor shops do to. I also seem to recall an online shop renting equipment.

I would not take one large pack and one small pack. I think it is a better idea to split up the shared equipment. With a long hike like this and limited experience, you should probably think about the possibility that one person will want to bail early and the other will not. Will you both leave the trail? Best to have that discussion earlier rather than later.