Each switch will operate 6 lights for a total of 12 lights.

Yes

Depending on the existing load and the anticipated load you may be able to do what you propose. Is this a 14 or 12 AWG wire and what is already on the circuit? What is the wattage of the new 12 lights? At 60 watts that's 720 total watts added to whatever else may be on the circuit. Incandescent? CFL's? We need some more info please.