12 V relay switch wiring
It's possible, using one standard relay and 2 push buttons per seat.

Four relays K1 - K4 are to be wired as shown for K1.
Each relay could be switched on or off with it's corresponding 'on' and 'off' push buttons. All the relays would go off together when the ignition switch is off.
Should 'single-button' operation be required for 'on' and 'off', the following ratchet relay based schematic would apply.