You will want to use a continuous light source if you cross-polarize, not flash, or else rig up some kind of modeling light. Start with no polarizer on your lights, and adjust the polarizer on the lens to minimize glare as much as possible. Then put a polarizer on the lights one by one, and adjust to minimize glare for each light. Trying to do this with flash only by trial and error is a huge PITA.
Use a circular polarizer on your lens, but linear polarizer is better on the lights.