Looping back down to London from Edinburgh in July

do you have reservations and tickets bought for Highclere? It is only open occasionally and tickets go as soon as they are released. You can't just turn up?

There isn't a direct train from Reading to Watford Junction. You could take a train from Reading into London Waterloo (catch a Northern Line tube train to London Euston) or a different train to London Paddington (catch a Circle Line tube train to Euston Square tube station and walk to London Euston.

Either way it involves the Underground and changing London stations.

Bus stop number 4 at Watford Junction for the knight bus.

Why would you uber to your tour when the knight bus is fast, cheap and frequent?

I've never rented a car in England, any recommendations?

Your profile doesn't say what country you are from, nor if it is one who drive on the left.

If you need an IDP for the UK you should get one. Especially if you are from India because it is not easy to get one in India.

If you are not used to driving on the left, or driving with a standard gearbox, you might study some youtubes.

Most signs here are pictorial but a surprising number of signs have writing on them. The National Speed Limit varies depending on the type of road and type of vehicle - it would be worth studying up on the laws before getting the car. The National Speed Limit is very rarely signed in numbers so you need to know it.

I’m from the US. My husband will be driving and has driven in England before.

We have not purchased tickets for Highclere or Stonehenge yet. Trying to figure out timing first. I’ll have to check on tickets to see if we can even go.

Any suggestions for places to stay other than Manchester?

If you want to stop in the north of England you have a number of choices. One would be Chester, a smaller city compared to Manchester but has lots of history. Another big city, with possibly more to see is Liverpool. Or you could see York. With a car you can see the Dales and visit Castle Howard or Chatsworth on your way south. They really knock Highclere out of the park (and it isn’t really a castle).

I’m not sure why you're using trains and car hire at different ends of your journey. It seems a lot of switching around.

Durham to visit the World Heritage site Durham Cathedral or in the world of Harry Potter Hogworts home in the Philospher's Stone. Or York which is a great and interesting part of the UK. Overnight then off to London by rail the next day.

Unless you are into larger cities and Manchester is a must I'd forgo an overnight.

Your destinations suggest you should examine a multi-destination itinerary, flying into north or south and returning from the opposite airport. It requires a multi-city search function to find a package, but will save lots of time at just about the same cost. I'm a gearhead and love Manchester's history in the industrial revolution, plus the array of South Asian restaurants. It does have a busy international airport.