July London/France travel

"3/4 days in London and Paris-is this enough or too much?" - I hope you mean 3-4 days in EACH. That is in both cases just enough to start, but, if you assume you are coming back, it will give you a taster.

Edinburgh to London is 4½ hours by train, one departure every 30 minutes. Times and tickets from the company that runs the trains, here: https://www.virgintrainseastcoast.com/
Tickets are a lot cheaper if bought in advance.

"Looking for advice on how best to travel to France and see if it makes sense to stop in Normandy." - The quick and obvious way from London to Paris is by train. Takes 2½ hours, roughly one departure per hour, Times and tickets from the company that runs the trains, here: https://www.eurostar.com
Again, tickets are a lot cheaper if bought in advance.

There is no easy way from London to Normandy, it requires train+ferry+train and is slow. The best way to see Normandy is to take a train from Paris to Caen, Bayeux or another town and pick up a rented car there.

From where do you fly home?
You have 3-4 days for London AND Paris? If thats your time frame, Normandy is out. You have only 1 ½- 2 days in each city. That's very rushed. My first trip to Paris, we spent 4 nights/4 ½ days, and that was satisfying. I would suggest sticking to London this trip and save Paris and Normandy for another.

I hope you mean you will have 3-4 days EACH in London and Paris. Otherwise, I'd drop one of them. Even 3-4 days each is short - too short if these include travel days to or from other places.

The easiest (and usually fastest) way between the 2 cities is the Eurostar train from St Pancras to Gare du Nord. This is direct and non stop. Going to Normandy would require a change of train stations in Paris and then another train to Caen or Bayeux. If you really want to spend time in Normandy, I'd recommend adding additional days (at least 3) on to your stay in France and stay there before either flying home from Paris or flying down to Spain.

Have you figured out your total number of days for this trip?

You can keep the costs down by undertaking fewer transfers. With only 3 or 4 days in each of Paris and London (I hope not total number of days), I would be tempted to leave Edinburgh for another trip, as you won't see much in 2 days and this time would be better spent in London and Paris, as you aren't going to see the main highlights here in your timescale. Tickets for the Eurostar are already available, so save money and buy your tickets ASAP.

Alternatively, drop France and stick to Ireland-Edinbugh-London, where there is enough to keep you occupied too!

If you are travelling after mid July, schools will be on holiday and prices will increase and availability will be more limited, so again book accommodation ASAP.

With four people to move around, train tickets in the UK (and to Paris) will be grotesquely expensive if you don't buy them early. We're not talking about a minor 25% or ever 50% price penalty here.

I, too, think two days in Edinburgh sounds short. Have you figured out how you're going to get from Ireland to Scotland? If you have 6 to 8 days for both London and Paris, I'd be inclined to add one to Edinburgh and use all the rest in London. Normandy's pretty much out of the question in your timeframe.

From what city are you flying back to the US/Canada?

We need more information before we can provide any reasonable answer. I assume you are flying to Ireland and home from Paris. If not, that is the first item to set. Normandy is not a reasonable day trip from Paris - to far. Really needs an overnight. But also the beaches are over 50 miles long from east to west. So if you want to see them, take a day. Since the kids are interested in Spain, how about showing them a map. Spain is absolutely out of the question.

Because of the variable price of the Eurostar you need to pin that down tomorrow. Late purchase tickets are very expensive.

We were in Ireland last summer and had a wonderful time. There's so much to see in London and Paris. Normandy might have to wait until another trip. Ditto with Spain. It sounds like everyone has their must-sees. Good luck with that.

Thank you all for your comments. Yes 3/4 days in both London and Paris. We are only traveling to Edinburg to visit a school and a cousin not for touring. Have knocked Normandy out. Will work on trains today. Is 4 days enough in London? Flying to Dublin and flying out of London.

As a slow traveller, I would drop either London or Paris so I could get to know the other places better (and, yes, pare down the budget.)
www.skyscanner.com specializes in one-way air fares and will show you a number of fairly cheap flights Edinburgh-Paris. If London, it's a coin flip whether to fly or take the train. It's a nice ride for those of us who like trains but air might be a little faster (counting delays on the ground) and cheaper. Whichever, buy tickets as soon as possible to save money. The teenagers will have lots of time to go to Spain on their own coin. Three weeks in Spain alone would make a nice jaunt.

...Is 4 days enough in London?.... For What? Four days is enough to get a quick overview of London. We have spent nearly a month in London over the past twenty years or so and still have not seen every thing we would like to see and, of course, there has been changes over those twenty. Some time this fall we intend to spend another week in London. It is really a personal preference for what you want to see.

You haven't indicated how many nights you have. If you are trying to keep your costs down the trip to Paris will be expensive since you are having to return to London. You might consider saving that for another trip. However, what are your thoughts/plan for getting to Paris? and from where?

If you want to stick with this number of cities then it would be logical to do Ireland > Edinburgh > flight to Paris > Eurostar to London

We've spent three week trips to both London and Paris twice so we've seen a lot of both cities but you can see quite a bit in three to four days in each. It's something of a Whitman's Sampler trip with a taste of each city. Pick out the big things you want to see and go for it. Consider getting the London Pass and Paris Museum Pass to help get past long lines. If you buy the passes in advance, you can plan which sites you want to see to get the most out of them. We did this the first time we visited each city and got a nice introduction.

We also use Rick Steves' guide books and follow the walks in his books. It's like having a private guide who lets you stop and linger over stuff you find fascinating.

A little planning can help a lot.

One more thought. The first time we went to London, we took our 20-year old son and his friend. We let him pick a lot of the places we went and they had a great time and we found much of it interesting. A couple of years later, he was no longer interested in traveling with us and would rather pursue his own interests. I'm glad we were able to enjoy a trip that we'll all remember fondly. And I'm also glad that my wife and I now travel as a pair and do all the things that we love.

Bon voyage.