As a store owner, it will mainly depend on what kind of weather riding style you guys will be doing. If you ride your tandem all day every day every weather then i would keep the disc brakes on and ditch the XTRs. If you only happen to ride when most normal people ride in a beautiful weather settings, you can go either or. Of course the XTRs will help in saving weight on your bicycle. IMO, disc brakes and v brakes are pretty much the same in the sunny, dry conditions. I hope this helps and keep on riding.