First you need to figure out is how much current it takes to light each type of lamp. If there is a type number on the base you can look it up on the web. If all you know is the Watt rating, divide the Watts by 12 or 14, respectively to get amps.
If you operate a nominal 14V lamp on 12V, it will be only slightly dimmer. I would just wire all three lamps in parallel and operate all three off the same 12V power supply.
I'm guessing you will need a 3 to 5A power supply. You could also just get a 120V (assuming US, why didn't you put your country in when you registered?) to 12V transformer and operate the lamps on AC.