We will be spending 2 weeks in London (our 6th trip). We want to get rail passes and take day trips to Windsor, Cambridge and Moreton in Marsh. Our newest Rick Steves England tour book says we can get advice on planning the best rail ticket for our plans. I don't know how to locate Rick's advice.
You might get more in depth answers if you posted this to the England Forum, rather than to England Reviews. This page is for folks to give their impressions of places they have stayed or eaten. Good luck.
Our info on BritRail Passes and tickets is at https://www.ricksteves.com/travel-tips/transportation/trains/britain-rail-passes. The pass that would most closely fit that trip plan is the BritRail London Plus pass for $139 per adult. If buying tickets as you go, note that same-day roundtrip rates can be similar to one way when purchased together.