One paddler has a better shot at rolling a tandem than two. The coordination
and timing are pretty critical and the two need to do this without
communicating (at least in conventional ways). It is not the length, nor
beam, of the boat that makes rolling one a challenge, it is the second
paddler.

Rick is absolutely correct. I have taken people out surfing in double
kayaks, and when we capsize I will usually just hold my breath and sit tight
until I can "feel" the other paddler wet exit, then it's quite easy for me to
roll back up.
In practice it's fairly easy for the stern paddler to roll a double if the
front paddler sits tight and simply leans forward and hugs the boat. However, I
find most of my "passengers" don't have this kind of savvy when the capsize is
accidental.

Scott
So.Cal.