aftermarket door locks

Relays are typically used to switch currents that the alarm output can't handle. If your alarm system can handle the current of the actuators, there's no need for relays.

If you do want to use relays, a multimeter (MM) would be nice. Assuming you got two leads from the alarm to switch the locks, these would normally be 0 Volts at rest (check with MM). When you lock, one of the leads will momentarily go to 12 Volts, then back to ground. When you unlock the other lead will do this.

I don't know about the colors you're referring to, but from the positions you describe, I think both relays are now engaged while at rest. You don't want that, because they'll be consuming a little power all the time, draining your battery. Easy to check by removing the wire to the alarm from the relay. If you hear it click when you attach it, it engages and draws power.

Assuming top = blue = 87, right = red = 85, middle = orange = 87a, bottom = red = 30, left = green = 86, I believe you need to change 85 (red) to ground to have the relays not draw power at rest. Then, wire the motors in parallel, between the two red wires from both relays. This should work.

If you have the relays and actuators wired as described above and shown below and the relays coils are activating, double check that you are using SPDT relays and not SPST relays. The numbers for each relay contact should be the same as those shown below.

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No, not possible, unless they're not getting enough Volts as a result of losses in the cabling. A multimeter will tell you if there is enough Volts available.

Make sure the mechanism is as smooth as possible. Service the locks, and make sure the actuator is aligned perfectly.

Sounds silly, but how about trying two actuators?