Like the others said, check with Guest Services and depending on where your sister in law lives from the port, call her when we dock. On
RCCL in April, we docked at 7a. From San Pedro to LAX is 30 minutes MAX on a Sunday morning. Of course if there's an accident, all bets are off!
With a 12:30p flight, you should be fine. You should also see if your airline and/or
DCL does the airline check in where you can register/check in the night before on board the ship, leave your bags out like normal, the next morning, claim your bags and then check them in with your airline at the port and you don't have to worry about your checked bags until you arrive home at your own baggage claim. That way when you get to LAX, all you have to do is go through security and get to your gate.