A bit of perspective rim vs. disc braking…
Heat capacity: Al:920 J/kg/C, Steel: 500 J/kg/C
Mass heated: Rim: 0.6 kg, Disc: 0.08 kg
Kinetic energy of loaded tandem (220 kg) moving at 16 mph: 5400 J
Temperature increase in components to stop tandem
2 rims: 5400/920/1.2 = 5 C increase (9 F)
2 discs: 5400/500/0.16 = 68 C increase (120 F)
If the riders are smaller and without gear, disc brakes may be sufficient. However, rim heat capacity is far greater.