I'm trying to get from London Heathrow to Edinburgh with my family (4 people), and can't figure out which option is the best trade-off between time and money - We arrive at LHR at 12:15.

Option 1: Fly from LHR to EDI - this is the easiest option, in that we're already IN LHR airport. It's more expensive, but there is a flight to EDI @ 2:15. I'm a little worried that we might not be able to get through customs in time to board, or we might get delayed, etc. The next flight out would be at 21:00, so We'd end up spending an entire day in the airport.

Option 2: Fly from Stansted to EDI - this is the cheapest option, since we can fly Ryanair, but the earliest flight is at 16:30, and I'm not sure if we can get from LHR to STN in time, plus there's the cost of the travel between the two airports as well.

Option 3: Rail from King's Cross to Edinburgh. If I get an advance ticket, and can get to KGX by 4:30, a one way set of tickets will cost me about as much as the round-trip in option 1, plus I still have to pay to get there.