We experimented some with tandem driving. Paul makes it look really easy, but holding two sets of reins and keeping the cues perfectly clear to each horse is anything but easy. We tried Theo in the lead the first time, but Theo was well aware that he was pretty much out of range of the whip we had and decided to mosey on at a leisurely pace with Thistle just about running him over. Thistle is more inclined to move forward, but he isn't the bravest of equine souls, which can be a problem for a leader. We'll be playing with this some more in the future.
I tried handling the reins for a little while and found it really hard not to oversteer. Oversteering one horse isn't too horrible. In a tadem it is easy to send the horses off in two different directions. I'll stick a second set of reins on the rein board one of these days and sort this out without frustrating the horses.