This whole question is amazing to me since, I've been in and out of the scene for more than a few years and sessioned in my own city, when I traveled and when Mistresses traveled to my city. I've only contacted Mistresses one at a time.

My gut feeling is that if you do contact two or three Mistresses for a trip, knowing you'll only have time for one, give them time to respond and be transparent if you already made an appointment.