My wife and I are visiting London the last week of July. We are arriving at Heathrow and staying at St James Court, a Taj Hotel, I plan to purchase two 7 day London Travelcard passes for zones 1 and 2. Since Heathrow is in zone 6, should I purchase an oyster card when I arrive at Heathrow so that I can take the tube from the airport to my hotel? How much should I put on an oyster card? I need to cover two people for both arrival and departure.