What fun! That’s a great idea and I’m glad to have given you the itch to do it!
There are lots of possibilities.
Firstly, you need to think about how many visits you want to do in the day. This also depends on when the cruise ship is scheduled to dock at Pauillac (or maybe they arrive there the night before?).
Personally, I like doing one in the morning and one in the afternoon, because each visit lasts at least 90 minutes and it gets pretty hot in the afternoon, but two in the morning and two in the afternoon is quite feasible.
Secondly, which châteaux you visit also depends on personal taste for the wines. But let’s assume you like them all.
Thirdly, you need to plan the trip in two halves because of the driving. It takes around 35 minutes to get from Pauillac to Issan, so it would make sense to plan one or two visits in the Margaux area and one or two in Pauillac/St.Julien.
I’m going to assume you choose two in each location.
If you choose to start in Margaux, Henri will take you from Pauillac on La Route des Châteaux, which is wonderful as you will drive past a host of iconic châteaux. You’ll see Haut-Bages Libéral, then the Pichons and Latour, then Beychevelle and the Léovilles, before getting to Margaux, where you will drive past Palmer on the left and see Ferrière, plus others I have forgotten.
In Margaux you are visiting Issan, which is a great choice. I hope Marion is still doing the visits because she was so good, but I’m sure you’ll have a great time anyway. Then you could either visit Giscours, which is open on Saturdays, or Ferrière. I visited Giscours last year and can thoroughly recommend it: Visiting Giscours + shopping at Sociando-Mallet
It was similar to Issan, in that you actually go inside the château, and the trip around the grounds in the golf cart was great fun.
I plan on visiting Ferrière this summer. It probably isn’t the same visual experience as Issan and Giscours but I’ve no doubt it will be extremely interesting. Ferrière belongs to Claire Villars-Lurton, who also owns HBL, and her husband, Gonzague Lurton, owns Durfort-Vivens. Therefore, I expect that Henri could get you a tasting of all three châteaux included in the visit, which would be fascinating to do. Chasse-Spleen is now run by Claire’s sister, Céline.
After all that, a good lunch is called for. I can think of two places - La Cave D’Ulysse, which is close to Ferrière, or the Relais de Margaux Golf Club, just down the road towards the river. Both offer wines by the glass (or at least did the last times I went).
In the afternoon, you could visit one or two châteaux in the Pauillac/St.Julien area.
I visited Pichon Baron last year: Visiting Pichon Baron
It is very impressive albeit a different experience to Issan, for example. You won’t go inside the château and it is quite a corporate set-up, but very professional and definitely one to consider. I haven’t been to Lynch for sometime but I would imagine it is similar.
Léoville-Poyferré as a wine is an acquired taste, as a visit I cannot say - I visited it 20 years ago and really enjoyed it, but it wasn’t the same wine tourism experience as other places and I doubt that it is now, simply because the original Léoville domain has been split into three.
I would certainly recommend Beychevelle, which I went to in 2020: Visiting Beychevelle
It is certainly corporate, but impressive, and the gardens offer a spectacular view.
Gruaud-Larose is also worthwhile - the view from the tower is magnificent. It belongs to Jean Merlaut’s group - I believe he is Claire Villars-Lurton’s uncle, although I’m not sure.
Lagrange is another possibility I have tried: Visiting Lagrange
The visit itself is not as visually memorable as others, and you won’t go inside the château, but the wines were brilliant.
Of the other names you mention, I would certainly consider Branaire Ducru, which I will probably visit this summer. All the others are fine, but not quite as compelling.
Of course, you could always start in Pauillac/St.Julien and head down to Margaux after lunch. One fabulous possibility for lunch in St.Julien is simply to get sandwiches from the bakery in Pauillac before heading to Port Beychevelle, which is what we do every year!
Anyway, I look forward to reading what you decide - again - what fun!