I cannot speak to all of your proposed ports, but i do know about a few. Lisbon is a wonderful city, but it is full of steep and not-so-steep hills and (in the rain) slick sidewalks. You will be able to use the elevators, but in our experience, Uber was a great solution. Very inexpensive and quick between parts of the city. Lisbon is full of small, largely accessible museum. I would recommend that decide whatever you think you will be most interested, plan it out, then consider 1.5 or even 2x the amount of time, just to make it easier on them. Le Havre was practically blown off the map during WW II and consequently, the reconstruction is decidedly postwar. it's pretty grim. There is a small, lovely impressionist art museum, but otherwise, I don't think it would be particularly fun for them. It's also an uphill walk from the port. Might be a good day for a ship's excursion. Popular ones from Le Havre include Rouen, which is easily walkable, and Monet's Gardens at Giverny, also very walkable. How long are you in port there? The lines say "Paris" but keep in mind Le Havre is a long bus ride from there. You'd be spending half your day just to get there. I'm not saying don't go, but consider your parents' stamina, endurance and patience. Paris is wonderfully walkable, but if they can't walk long distances, you'd have to scale that back of course. As far as London, same thing. Think about how you will get from Southampton to London. The train runs regularly, and there are busses, but if you are carrying considerable luggage, you might want to take the easy way out and take the ship transfer to London. They all go to Heathrow, some also have city stops, depending on the line. Are you staying in London after the cruise?
