Would love advice on this itinerary

By my count, you are traveling and switching hotels 13 out of 15 days. This would not be an enjoyable trip for me or most people. I think you need to cut out at least half your stops to have time to actually see these places. Maybe focus on Scotland or England, but not both.

I am curious about Day 10- drive to Banavie and take the steam train.

The train no longer picks up at Banavie, so you have to join her at 1250 in Fort William, to get back to Fort William at 1852. Then on to Glencoe- a long day.

That is a long day as you'll have to leave Skye early to be in Fort William by noon to give yourself a comfort factor.

Secondly, there are doubts over whether the Jacobite will be able to run this year, due to the ongoing door locking problems. My own guess is they may be able to find coaches to run the morning train, but the afternoon one may be in doubt.
Only time will tell if even my scenario plays out. Worst case is that no steam trains at all will run. It may be Easter before any definitive answer is known.

Loch Lomond to Keswick is about 3 hours with a brief break en route. So you get 1/2 day there on arrival day. Keswick to Liverpool is 2 hours on a good day- allow more like three. So you may get an hour or two in Keswick on departure day, then maybe half a day in Liverpool, and an hour or two in Liverpool next morning.
In neither place is that time to do very much.
Both K and L deserve more- barely scratching the surface.

York is the same- barely any time allocated to the City.

This is a pretty relentlessly fast pace. Where are you from?- the UK or overseas- to be starting from Cambridgeshire and ending in Liverpool (to 'Home').

On Day 3, if the low tide is at the wrong part of the day you may not get to Holy Island until after dark. Then you leave next morning. And you don't really want a car in Central Edinburgh.

Please I am not trying to be harsh, but this needs a bit of a rethink IMO.

Thank you very much for your replies. Yes it is a lot of driving but this is meant as a driving holiday. The stops in England are really just to break up the drive/pop in on family, rather than discovering the areas. I agree Keswick, York etc deserves more time but we already know the areas fairly well so it is really just a place to stop on the way up and then back home to Cambridgeshire. Holy Island is somewhere we haven’t been to but may take that out of the itinerary if the tide makes it difficult to visit in our timeframe, thanks for the heads up on that one.

Would you recommend staying just outside of Edinburgh rather than driving into the city?
We were thinking of staying in Banavie, as it was recommended as a nice place outside of Fort William, but we were hoping to get the Jacobite from Fort William, will look into this nearer the time to make sure it is still running, thank you for that information, that is something to look out for.
We have also opted to miss out Dunnottar Castle and to go instead to Aviemore from Edinburgh and then on to Loch Ness the next day. So really the advice we are looking for relates only to the Scotland part of the trip starting in Edinburgh:
Day 1 – Edinburgh to Aviemore (127 miles)
Day 2 – Aviemore to Loch Ness (42 miles)
Day 3 – Loch Ness to the Isle of Skye (102 miles)
Day 4 – discover Isle of Skye
Day 5 – Isle of Skye to Banavie (99 miles) – Jacobite train if possible and then on to Glencoe (19 miles)
Day 6 – discover Glencoe
Day 7 – Glencoe to Loch Lomond (60 miles)
Would love any advice as to whether this looks like a decent itinerary for a first trip to Scotland? Would we be better off on one of the well known driving routes such as Route 66? Thank you

I would definitely recommend not driving in Edinburgh. Parking is very expensive, almost all hotels charge for it, and the bus lanes and trams make it tricky. You could consider the Hilton Doubletree at North Queensferry which has easy public transport options into the city and puts you the right side of the city for your drive up to Aviemore. There's a wonderful restaurant called the Wee Restaurant in North Queensferry too. It's a nice walk downhill from the hotel and they will often offer a ride back up to the hotel, or call a taxi for you.

You're only allowing yourself one full day on Skye even with 2 nights, which means you won't see much. I get that it's a driving holiday, but you'll have to be very selective and bear in mind that it's slow driving here as many of the roads are single track with passing places. Not sure why you'd need 2 nights in Glencoe if you're not going to do lots of hiking. Maybe spend an extra night on Skye instead?

Thank you, will look to book the Hilton at North Queensferry, that sounds perfect and will check out the restaurant, thanks, its really useful to get recommendations. We have limitations on mobility so will take your advice on an extra night on Skye, thank you very much.

These are the Holy Island safe crossing times -so you can see if it works into the date you are proposing to be there- https://holyislandcrossingtimes.northumberland.gov.uk/Default.aspx?dt=0524

One other possibility, if the Jacobite runs, is to drive to Banavie from Skye. Park up at the hotel. Take the 1219 diesel train to Mallaig. You have 30 minutes there, then catch the morning or 1st steam train back at 1410.
Yes you have to buy a return steam train ticket and forego half of it, but...

That gets you back to Fort William at 1600. Then bus or taxi back to Banavie in time for dinner. If the steam train doesn't run then get the diesel train back to Banavie at 4pm. The benefit of that plan is you see the unusual railway swing bridge over the Caledonian Canal at Banavie open and close.
And you see Neptune's Staircase- the lock flight that lifts the canal from sea level.

Brilliant advice, thanks so much, that is really helpful

I'm curious why you decided on Aviemore. I stayed there for a few nights in April. The town is pretty underwhelming. It's not a bad base for exploring the Cairngorms, but there are prettier towns to stay in nearby. Maybe look into Kingussie or Grantown-on-Spey.

Thanks, I will look into those. I chose Aviemore because it was recommended by a friend who goes every year, saying that though, I dont think she usually goes outside the area so would probably not know there were other places nearby to look at, thanks very much.