First trip to England/Scotland/Ireland

Since you want to spend a couple of days (2 nights would really be only 1 day) in London before heading to Edinburgh, you're better off taking the train if only from the time perspective. It takes only about 4-1/2 hours. Dealing with airports would take longer. The trains for Edinburgh depart from Kings Cross Station.

Tickets for August/September aren't on sale yet. You might keep an eye on the NationalRail.co.uk website, because you'll be able to save considerable money on Advance tickets if you buy them early. Be sure you understand the cancellation/refund limitations.

Have you thought about catching the sleeper train from London to Edinburgh? (Departs from Euston not King's Cross).

Definitely take the train between Edinburgh and Inverness. There are plenty of trains to choose from. Use this website to book your ticket before you travel to get the best deal.

if the scenery in Scotland is valuable - and I suggest that it is - and a couple of actual days in London is important to get a start - you could take the Sleeper all the way from London to Inverness, which gives you the comfort of your sleeper room all the way north. A much calmer start to the day. https://www.sleeper.scot/

You can board and settle in as early as 8:30pm and you leave London at 9:15 pm M-F (doesn't run Saturday night) or 15 minutes earlier on Sunday, sunrise between Perth and Pitlochry, and nearly 3 hours of beautiful scenery to an arrival in Inverness at 8:42. What's not to like? After arrival there is the Club Lounge on Inverness station with showers, snacks, and relax before heading into town. Onboard there's a pretty decent restaurant with modest to moderate prices.

Throughout the UK there is always a schedule reissue in May and December, so times in August and September may be slightly different.

Much more relaxing than a flight and then a regular train, and even a daytime train will be too, and the daytime one does have the advantage of scenery in the Borders.

Both the day and night train are much more environmentally friendly than flying, and much less hassle. The daytime one is faster than the flying experience. The night one takes longer but you have your hotel with you.

Have you looked into flights from Inverness to Dublin to see if there are any? If so it would be your choice, if not then it would be Edinburgh.

Fly from Edinburgh to Dublin. A short nonstop flight.

No nonstops from Inverness.

Thank you, EVERYONE!! This is all so very helpful. I had no idea there was a sleeper train and will definitely look into it. It might actually make the most sense to go straight to Inverness - I hadn't thought of that since I had wanted to at least see Edinburgh but maybe we can add it on at the end since we need to fly from there to DUB anyway. I'll probably be back with more questions once I start looking at actual flights. Right now they seem all over the place in price and time so I wanted to get the itinerary mostly in place first.

You all are GREAT - thanks again!
Peggy