We’ve both road and mountain tandems 🙂
When I ride the road one now, it’s a bit scary compared to the stopping power on the mountain tandem – which has slx front and back with 203 (?) rotors. We stop well (too well – stoker told me I was going downhill too slowly last week).
The road tandem has four brakes. Canti’s controlled from the front drops, a rear hub, and a rear calliper controlled by the soaker (when told to brake!). Key thing here i s that the cantos are matched to the drop levers, which are designed for cantis, as opposed to a calliper brake. And use high quality pads, checked often!