good job going out there! very impressed.
just a thought though, on that last ride, when you couldn't keep up and you are figuring it is b/c they are intimidated.
What about it being overtraining? not resting inbetween your big rides and that ride.

I know if I was to do what you had done my legs would not be taking me anywhere!!(last year I was riding my bike, doing spin classes, and riding the horses and I had the same problem that you did! I have now dropped the spin classes and make sure that I have 2 good off days a week from everything)