2 Week UK Itinerary Help Please! Is this realistic?

I am not so about so many one day visits. But I am very much encouraged by your slow travel and taking into full account your travel days which will get you into a much better position to see what it is that you want to see when you get there.

good luck with your trip

There are some lovely walking paths around MiM to the surrounding villages like Blockley (where Father Brown was filmed), and near Oxford i recommend Woodstock. If you're keen on Royal Palaces, Blenheim Palace is there. Some nice pubs and footpaths out there as well, such as Blenheim Common --> Stonesfield.

My main concern here is that some of your destinations are far away from one another, ex. Cotswolds (MiM?) to Windermere would take a significant amount of time with at least two changes on the train AND if CrossCountry trains decide to behave!

Take some more consideration of the travel times between the destinations you've outlined and make sure it's something you're alright doing. I always find being on the train is the most exhausting part of any trip since you're not moving around.

From recent experience where we made a similar itinerary except by car, if I had to do it over I would definitely not include the Highlands. Even without it there's a deceptive amount of distance to traverse, which can be further complicated if you aren't hiring a car and thus need to navigate the logistics of trains and busses.

Is this a family trip? If so, what are the ages of the children? This looks like a scenery-heavy trip; I don't recall enjoying that sort of thing very much as child, but of course every kid is different.

It's highly recommended that you stay outdoors and walk around as much as you can on your arrival day. That will help vanquish jetlag. Sitting on a bus would put me to sleep within 5 minutes.

You've allowed only one full, hopefully-not-too-jetlagged day for London sightseeing. That is incredibly short for a first visit.

Bath, the Cotswolds and Oxford are all in the same general direction. It would be a lot more efficient to spend 4(?) nights somewhere in that area rather than making separate trips from London to Bath and the Cotswolds/Oxford.

The Isle of Skye is in no way a day trip from Edinburgh. You really need multiple nights on the island, plus the time to get there and return.

I would take your additional days 12, 13, and 14 and move them up to the front so you could add them to London. You have no time for London, and it deserves so much more. Leave the Highlands for another trip.

Then I would take the advice above, and instead of taking day trips to the Cotswolds, move your base there for a few days. The Cotswolds is very near to Oxford, so you could easily do a day trip to Oxford from someplace in the Cotswolds. I doubt that you will have time for any punting in Oxford unless you make time for it and skip a lot of the buildings, which would be a shame. Oxford is beautiful, and it will take you a whole day just to see the sites of interest right in the city. And don't miss the Ashmolean Museum in Oxford, which is a wonder.

The rest is all doable, although, as acraven asked, it would be helpful to know who all is going on this trip.