You guys are over-engineering this. In the end, after all the clandestine operations to not leave a paper trail, you still have a mysterious extra phone in your possession. What would your explanation be if that phone was found?
It's seriously not that hard: register a google voice number (or similar), and use a private web browser session to open up texts and send/receive. When you actually go to a session, if you don't want to be "followed," turn off location services on the phone. If you want to make it look like you're running errands or something, drive to Home Depot, turn off location services there, then drive to the appointment.
Questions about why you're not on the family-stalker app? "It was draining my battery so I turned it off"
I mean, what do you do with your phone when you hobby anyway? Leave it at home?