It would be very hard to control a v-brake and a drum brake with the same lever because they need very different amount of cable pull. On the other hand, it is possible, though not recommended, to control both v-brakes with one lever and the drum with another one. In fact, most manufacturers have veered away from such a setup because it's not optimal.
Here are a few solutions.
– Leave it as is.
The drum brake isn't the best brake but it is very good tool to slow you down, especially on long downhills where the rim brakes could overheat. So your stoker will never use it except
when going down a steep hill. You then tell her to apply it in a continuous fashion all the way down, and you use the two rim brakes to fine tune your speed.
– Install three levers up front,
. The left oblique lever controls the drum, the left straight one controls the rear v-brake and the right one controls the front v-brake. That way, I apply whatever brake I want. Great for steep bumpy hills because it allows ideal modulation. But on very long hills, I' would have to brake all the time.
– Use a shifter to control the drum brake.
Some use a thumbshifter, others a downtube shifter. The idea is that you use the shifter to partly squeeze the drum and leave it that way until the hill is over. It's great in those 20-km hills that you have out West because you don't have to squeeze it all the time. Once it's applied, you simply use the two other brakes when in need of more slowing or stopping power. The shifter could be either on your or your stoker's handlebars. As strange as it may look, this solution is looked favourably by many people, especially out West.
– Remove it!
Depending on the weight of your team and your riding plans, you may not even need one. Some teams have crossed the Rockies without a drum. I would not do it, however.
As for tires, you could likely, depending on the width of your rims. Sheldon Brown has a good table on that, but basically if your current tire bulges (i.e. is wider than the rim), you could go to 1.1 or 1.2 inches. However, unless your team is very light and/or your roads very smooth, I would stay with 1.5". Get high pressure slicks and you might have a pleasant surprise.