You really do need a car (unless you go on a coach, which you don't want to do).
The crossing to Caen gets you nearest to the D-Day beaches, but Cherbourg is not too far either. It's a bit more of a drive down from the Calais ferries (or eurotunnel), but still easy enough.
The car will hopefully be a go, he's learning to drive at the moment and it looks like he will have passed in the next few weeks (fingers crossed). I guess it would be best to drive as suggested and get a private tour?
Drive and do it yourself is my thoughts. Arromanches is the hub. For other things to do, there is Bayeux for the tapestry and Caen a modern city. Would you be going via the tunnel or the ferry to Caen/Ouistreham ?
We had a long weekend there a couple of years ago, Greedy, drove up from Poitiers.
There is a huge amount of info. available from the tourist offices and on line - you can easily plan your own agenda. Walking along some bits of coast you just find the defensive structures as you go. Whilst the American Cemetery is impressive and a walk on the beach brings home the difficulties of the landing, don't miss the smaller, scattered cemeteries. There is a very good museum at Arromanches. Watch out for the speed cameras in the outskirts of Caen!
Please buy the Michelin Map No 102 entitled Bataille de Normandie. About £6 on line. Fantastic reproduction 1947 reproduction map of the seaborne and airborne landings. A must if you are exploring by car but obviously no use as a modern road map.i stayed at a Haven Holiday site in Normandy and visited the lot of major sites . Will post further details when I get home. Have a great visit.
Word of advice.drivers new and experienced are well advised to steer well clear of the famous Normandy Calvados which reminds me. Go on line and find out what you will have to carry in your to keep the gendarmerie sweet. Spare bulbs,reflective jackets,breakdown warning triangles,breathalyser kit from Halfords,first aid kit,headlamp beam converters,all vehicle and driving documents etc etc
Yes, remember to check all the stuff you need to drive in France. It is 2 breathalyzer kits in the car and a reflective 'jerkin' for each person in the car. Not sure why we have to carry spare bulbs though - it cost a fortune and a garage had to remove the bumper off my car in order to put in new bulbs. I don't think I could take off a bumper by the side of the road - or anywhere!