I have an older NRS SB Raft that's just under 10' long, about 6' wide with two thwarts. Similar in design to the following:
9'6" Otter Livery 96 Rafts - Std.
It works great as R2 and is highly manuverable but feels small with more than 2 adults - at least those of my size. I prefer to R2 riding the tube one leg in, one leg out. No room for me to do that in the bow or stern - as you can see in the link above as the thwarts leave little room in the bow/stern.
I have a frame (54" wide) that works great. My 3 boys fit great on the front bench (picture below) but it can be snug for an adult to ride on the front bench (missing in photo) depending on the size of the rider - let alone two riders.
I took the raft and frame down the Middle Fork of the Salmon this summer in early June (medium high flow) for a friend to row and the raft did great. We only had one rower and no riders, with a 5 gallon water jug and two drybags in the bow for some additional weight. It flipped twice, but that was due to user error hitting the meat in Velvet and Devil's Tooth.
The raft is small enough it's easy to self correct - numerous flips on the Middle Fork were avoided by digging in an oar and giving a forward or reverse pull.