I don't know how to use relays Can you please explain how to use them? Can they handle currents upto 15 amps?
Lots of info on the net on relays, Here is a good tutorial on the subject
Relays come in a multitude of current ratings.Here is a wiring diagram
Forgot to mention the 12 diodes you'd need, but I gather that you wish to make it non-electronic due to lack of knowledge(?) of how to do it, but diodes are very easy to use.
Their purpose is: D1 to D4 are for protection of the switches against inductive kick back from the relays and D5 to D12 constitutes what is called diode logic, that routes the switches outputs to the correct relays.
It will take two switches with each 3 positions (single pole though) and if wired as shown, should work as you specified. Remember to add a fuse in the +12V line from the battery.
SW1 could be one with a spring return to the center position.
SW2 could be a 2 pole switch with center position off.