Well if you plan on going to some English Heritage venues, you can get them an Overseas Visitor Pass which will save them loads of money!
Basically you buy a pass and it will pay for itself when you visit 2 or 3 venues.
I have had an EH pass for year. I love being able to visit places and knowing I am getting a deal. I switch off between National Trust and English Heritage because you get to see different things between the different organizations. Either of them are well worth it especially if you want to get the most of your time here in England. Also you can get a discount on some places in Scotland.
Seeing England doesn’t have to be expensive!
All the Best!
American to Britain