London Travelcard

Heathrow is in Zone 6. Neither Heathrow Express nor Heathrow Connect accept Travelcards or Oyster. Hampton Court is in Zone 6. Trains, which originate in central London at Waterloo (zone 1) and are either direct or change at Surbiton (zone 6). Trains to Hampton Court are included. Windsor is a little more complicated. There are two stations. The first, Windsor & Eton Riverside is served by Southwest Trains from Waterloo. There may be a change or straight through. It is outside the zones, if you have a Zones 1-6 Travelcard you will need an extension ticket from the Boundary Zone 6 or Feltham. The other station is Windsor & Eton Central, served by First Great Western from Paddington. You will need to change at Slough. It is outside the zones, if you have a Zones 1-6 Travelcard you will need an extension ticket from the Boundary Zone 6 or West Drayton. These are easiest understood by reference to the former - still available - London Connections map or its replacement and more current London Rail and Tube Map. If you scroll down to the last map on the Station Interchange Maps you can see the relationship between the two stations.

A six zone Travelcard will cover you to Hampton Court but not to Windsor, which is completely outside the Travelcard area. For Heathrow it will include travel by the Piccadilly Line underground but not by the Heathrow Express/Connect trains to Paddington. I would suggest using Oyster pay-as-you-go money rather than getting Travelcards, as the daily spend is capped at the cost of a Travelcard. You will still need to buy separate tickets to go to Windsor, or to use the Heathrow Express/Connect.

Thanks so much for your responses, it has been very helpful.
Cheers!