Caroline, I appreciate it that you get your back up when you see your plan discussed and suggestions are made that you don't like. I'll try to see if I can make the original request work, using the trains. I don't know what time your boat gets in at Barcelona, but shall we say early morning in time to catch a train by about noon? And that you want the fastest, most direct trains? And that with about 7-9 days and 3 further cities to visit we will say the remainder of 3 days, 2 days, and 2 days, and you fly out on the next - so all that final day will be dedicated to getting home? So - Day 1 - arrive AM in Barcelona, get to station. 2 possible trains to Paris: can you get to the station by 11 am? The first possible train is at 11:16 and arrives at Paris Gare de Lyon at 20:45 (8:45pm), with changes at Cerbère and Montpellier Saint-Roch. The second possible one leaves at 16:15 and arrives at 22:45 with a 12 minute connection at Figueres. So no time in Paris on day 1. Day 2 - Paris. Day 3 - transit to Munich - you couldn't pick so I've given it a go.
9:10 train from Paris Gare de l'Est, arrive Munich, with one 15 minute change in Mannheim, at 15:28. Get to the hotel and check in, time for dinner and evening in Munich. Day 4 - Munich Day 5 - transit to London 7:38 train from Munich to Cologne, change to Thalys to Brussels, 1:24 in Brussels to make the 30 minute minimum check in cut off for Eurostar, arrive in London 17:03 at the height of the rush hour to get to your hotel. Evening in London. Day 6 - London Day 7 - LOndon Day 8 fly home. I wouldn't do it but if that's what floats your boat go for it. I'd fly and limit myself to 2 cities.