I've used 25 amp relays in several different uses and applications, you can to
You can use the OEM wires to activate the relays (battery input to the on side of the relays) and use a bigger battery feed wire to all four relays, each light circuit or individual battery feeds to each relay
it is your choice on which way to go, None of the light circuits should have a large current draw so using a #4 up to a #8 gauge battery feed size wire to feed all the relays individually should work well
I would mount the relays in the trunk next to the driver's side taillights on a homemade bracket and tap into the trunk wiring harness there to do this job I would remove around one inch of the wire insulation, don't cut them apart, and then wrap the new wire pigtail going to each relay and solder and heat shrink insulate each joint