Ask yourself, why ride a tandem? There is the fast, drafting stuff which we could care less about. It is because of the shared experience of riding together. Riding with fun and enjoying the sights is initially strongly connected to an understanding of abilities. That takes times to figure out and requires talking about stuff and adapting. Talking and listening about stuff during the ride and after. Cadence is one element, which can be aided with different crank lengths. Good luck, I hope you can slowly earn your stoker's confidence again.