I have only been on one 'club' ride but I do now they have two groups. The A group that is very fast (strenuous on Snap's list) and the B group which is everyone else. They leave from the same place but travel different routes. Because it's hilly around here the people get separated on the climbs but there are regular meeting up points. I would say this group is moderate to hard/moderate. These groups have men and women though so that's part of the reason they separate a little.

I'd let the super fast ones in your group take off and not worry about staying together. Then have a leader for the rest and keep them together. If there's a LOT of disparity in that group, then maybe have two groups/paces for them as well.