Hey Phil,
Good job on securing lodging in Ouray, not an easy task! Regarding to trail comm, your FRS radios aren't designed to hit the HAM freqs. As suggested, please pick up a Baofeng HAM radio for comm with the group. These things are pretty inexpensive on Amazon!
This group has switches over to HAM years ago. The cool thing is that you can use the CB antenna mount and coax just not the actual antenna. So, if you've already run the wires from the front to the rear of your rig, a simple antenna swap might be all that's needed. On the front end, you might need a tiny connector adapter called SMA adapter to go between the Baofeng radio antenna port and the vehicle antenna coax.
An externally mounted antenna will allow a hand held radio operator to communicate effectively with the group as the terrain makes it challenging to have a line of site between vehicles.
As far as which trails, that is TBD based on weather, group size and ability. We'll setup daily trail rides in the morning during the driver's briefing.