I'm trying to model a mtb tandem, and what I did was create the captain seat tube forward in one model, and the stoker seat tube back in a second one. I don't need miter templates, but I will need angles and lengths for front and rear of the bike. Then I'll simply fill in the middle by using whatever length of boom tube I decide on, and then fit the lateral and stoker top tubes as needed. Since the boom tube is generally level, using the same BB drop in both models would seem to give me a useful model to follow.
Does this make sense, or am I asking for trouble? For whatever it's worth, this is my first tandem build, and it's really just intended to take my grade school age kids mountain biking with me. Of course I'd like to aim for accuracy, but in reality, as long as it's safe, it's going to be good enough. Ending up with the correct head tube angle is probably my main goal.