Motors are the easy part. They need to be controlled. You need to be sure hat you vcan pulse them in one direction for about half a second to lock, or in the opposite direction to unlock. Applying power continuously will flatten the battery and maybe make a mess of the motor. So you need a controller for this. This may be able to take a signal form the alarm. If not a lock/unlock switch is needed in the drivers door motor. You will then need to lock and unlock from the outside using the key.
Then you can do about the wiring. That is the easy part. I suggest a dry run first before you disturm the doors and wire it up Just make sure the motors work as expected. If so, go for it.