This is one thing you can do.
Run a short piece from each relay, and then run one wire back to the fuel pump. The wires can be joined like a Y. At the Y, you need something you can crimp the three 10 guage wires together and then solder them together. It will take a fair amount of heat to solder the wires, and solder will wick up the copper under the insulation. Where the solder stops wicking, this is the place where the wire could break if it sees any vibration. So add a number of layers of shrink sleeving over and well past the joint to give it some strain relief, and support the wire so it won't vibrate.
Also, actuate the relays separately. If you run both relays all the time, you will never know if one fails. So if both fail, you would be no better off then if you had just one.