Depending on how long you’re in Ireland, the west isn’t all that far from the east! Your biggest thing is going to be making sure one of you is the reminder to drive on the ‘right’ side of the road. Also, in case this matters, the majority of rental cars are standard… i.e. the shifter is on your left hand side…. You need to make sure you request (and will have to pay extra for) an automatic if necessary.
Look into Eurail passes!
Look into flights, especially munich-greece.
I would also say fly dublin (or maybe shannon or kerry) to London. Honestly, the “novelty” of taking the ferry can quickly wear off.. especially if it never shows, get’s “docked” for weather, or the water is too rough. I highly suggest flying that route! It will also save you a lot of time and you really won’t miss much scenery. Also, the way the weather is, you may not see Ireland once you’re 100 yards out! lol
I would say train for all the italy/france/spain parts.
Also know, everything is subjective. I appreciate what Florence has to offer, but to me, Venice is worth at least a day. I think we spent maybe like 5-6 hours there… and while it would have been nice to stay longer, it was one of the highlights of all my european travels and I was satisfied. We stayed overnight in Florence and the only thing that was nice about it was seeing David…
Rome, know that you can’t choose just “2-3” highlights. Skip the sistine chapel (it can take hours to get in). Definitely run through St. Peter’s, Don’t go INSIDE the coliseum, it’s a waste of time and money. Spend time in the forum and if you are christian spend time in the churches and basilica’s. You can see the pillar Christ was scourged on, his manger, the table of the last supper, chains that held certain apostles, the nails, and so so much more. It’s amazing also to see the “underground” churches. If you can plan enough in advance, try and take the vatican’s “scavi” tour. You need to plan this asap in advance, can’t do it once you’re in town. It’s the excavations under the vatican and even has Peter’s bones… pretty neat stuff. But, again, it all depends on what is important to you and will take a LOT of advance planning. It’s a large city and takes a while to get around… and everything is so amazing you don’t want to leave it!
Paris, I could care less about. Not a fan ;-0 I hear you either love it or hate it… I was in the later group.
London – My second home. My parents live there and it’s pretty amazing. It IS expensive though! Unless it’s really important to one of you, skip a lot of the tours… but make sure you make it around to see everything. (Also keep in mind, “London Bridge” is not the right bridge. You want to see “Tower Bridge.” 🙂 Also, the London Eye is pretty expensive, and honestly, I don’t think it’s worth it…
The 2 places not listed I would rec looking into for alternatives if something doesn’t work out, is Prague and taking a train through Austria and time in Salzburg. I think Austria is one of the most overlooked EU destinations out there. It’s my favorite country out of the 15 I’ve been too worldwide…
Keep hydrated and make sure you can say hello and do you speak english in the local language! You’ll get much further asking in their language than you will in English…. Most know English, but appreciate the respect of not assuming they do. 🙂