TSandM:
If one (or God forbid, BOTH) of the other divers have cameras, it makes it that much worse.
Actually, one of the best 3 person buddy groups I've been in was with two women photographers. One would take photos and the other would be a fish spotter. The next dive they'd swap. I dove with them for 3 or 4 days in Cozumel. They moved at the slow pace I liked. They both had great air consumption so we had nice long dives. The spotter and I typically wandered around at fairly big buddy separation distances, but paid good attention to each other and the photog. The photog re-established eye contact after every shot. You know that everyone has good situational awareness when you spot something, and without taking your eyes off it you raise up a hand, then almost instantly there are two people hovering beside you.
OTHER GOOD 3 PERSON TEAMS:
1. Me + a couple that were very new divers. I led the dive, they stayed abreast and behind me. They kept track of each other, and I set a pace where it was easy for them to keep up with me. I'd alternately check on her, and then next time look at him. As it was around their 5th dive after certification, they stuck on me like glue.
2. 3 experienced divers, meeting each other on the boat for the first time. The dive was on an easy to navigate, very well defined spur and groove reef. Shallow, so gas consumption was not relevant. Although for each of the dives, we had a "lead diver", in reality we just agreed upon our general path and did a group wander with each diver keeping track of the other 2 at all times. It was almost as if there was a "center of gravity" to the group. If one diver got intrigued by something off in one direction, the other 2 kind of got pulled in his direction. OTOH, each diver also kind of bumped into a wall of increasing resistance as he approached the limit of visibility w.r.t. either of the other 2.
SO-SO 3 PERSON TEAM:
I'm insta-buddy to an established buddy team. They have good buddy awareness with each other. They are relatively unaware of me.
BAD 3 PERSON TEAM:
I'm insta-buddy with a husband & wife. He will lead the dive. We agree upon the general area we are going to look at. As soon as we hit the water, he takes off in the opposite direction, at a pretty good clip. Most of the dive is me and his wife more or less abreast, enjoying the dive, while he is disappearing into the haze. 3 or 4 times I fin hard, catch up to him and grab a fin to stop him. The wife stops when she hits the agreed upon turnpoint pressure. Again I have to chase him down when 15 seconds later he is going out of sight and shows no sign of stopping.
I was very happy when during the SI she told me that her husband wouldn't be diving with us on the 2nd dive. I asked if he had ear problems or something and she replied something like "No. I told him to go find a different buddy."
My guess is that he was an atrocious buddy even in just a 2 person team.