So, I'm confused. Did the timing chain derail, or did the Stoker lose the pedals because of a lack of pedal retention? It matters. There seems to be a tendency to overreaction on the parts of both Captain and Stoker in the o.p. Buying e-bike chain seems excessive since there isn't any indication that a new 'normal' chain wouldn't be adequate. The part about a "high cadence stretch" has me wondering about the Captain's ... sensitivity, if you want the truth. The Stoker may not be overreacting. Captain, we need to talk. At this point I'm pretty sure your problems are not of components and their quality or tolerances. We need to know more about how y'all's came to own a tandem, how and where you want to ride it and ... other stuff like that ... or not. But I think it could help. FWIW.