We sympatize with all you Santana owners with Winzip brakes.
If they are that troublesome/dangerous, then return tandem to the Santana dealer for a full refund.
Have used centerpulls, sidepulls, cantis, Self-Energizing, U-brakes, V-brakes, drum and discs in varying combinatioins and have NEVER had to adjust brakes/pads after/before descending any hill or mountain. Have desended 6% 11-mile-long switchbacked moutain with Mafac cantilevers only . . . no issues except for cramping fingers!
Our personal tandem does not have discs or any type of drag brake . . . and we live in relatively hilly/mountainous terrain.
We consider ourselves relatively experienced with over 212,000 miles as a tandem team but are by no means 'experts.'. Have ridden 30 +/- tandem brands/models from A to Z (Assenmacher to Zona) and many in between (including 'tana's Arriva, Sovereign, Ti, Beyond).
It's up to the manufacturer/dealer to back a product if it does not perform as advertised.
Again, we sympathize with you WinZippers!