This is, once again, based loosely on a RL situation with my nephew Jake's friends, the Cowells. Having three growing boys, so close together, has been something of a challenge for the parents, and both of them have come to me -- not for advice so much as to bounce ideas around. That's how I came to hear about this incident.
From what I understand, Ivor's answer was very close to what happened in real life. David also has a good point, which might be considered.
This was a quick discussion we had at the Thanksgiving Leftovers Massacre Friday night, so we didn't go into much detail, but part of the problem is (IMO - based a bit on observation and a LOT on having seen other situations) that 'David' (Glenn, in real life) feels left out, because he doesn't have his own twin brother. The rest of the problem is that Mom and Dad aren't able to deal with the kids the same way (going back to the first BOTD - Dad can fit both twins over his lap, but Mom, the smaller partner', can't).
In my household, if boys get in trouble together, they get spanked together. I reminded Mr. C of that, and he said he considered it, and it probably would deal with any questions the boys have, but he hadn't wanted to make a snap decision.
I'm sure there's also a bit of trouble brewing from the idea of the eldest having to wait for his session, and that's another layer of 'unfair' for Glenn. Maybe they should just let all three boys game for position next time?