It's really VERY EASY! Just drive to the port, tell the security people you are dropping luggage and then returning the rental car, you go to curbside where porters are waiting for you. Get out of car and put luggage on curb (they will be right there so no searching for someone). They will make sure all bags are tagged, you tip them, get back in the car and back to the hotel. Keep your carry ons with you of course. Get on the shuttle and to the port and check in!
I have to add this is the greatest vacation a family can take (IMHO). We have done it twice and all the kids are begging to go back! The 3 year old literally cried on the way off the ship.
Don't sweat the small stuff ------ have a great time!