Does anyone know how to get from Heathrow to Stansted airports using the underground? For example, can we take the underground from Heathrow to somewhere in London and then a bus or train to Stansted? Thank you all in advance!
Take the Tube from Heathrow to Stratford and a National Express bus from there to Stansted. This page on the London Toolkit site tells you exactly how to do it.
Or get the Underground to London Liverpool Street station and then a train from there to Stansted. They run every fifteen minutes.
I would be extremely unwilling to get road transport from anywhere in central London or the inner suburbs to an airport any time except the very early morning or late evening. There's just too much chance of bad traffic delays.
You also can take a National Express bus directly from Heathrow to Stansted. That is the fastest route.
Whichever means you use to get between the airports, the most important thing is be be sure you have at least five hours (six would be much safer) between your scheduled arrival at Heathrow and your scheduled departure from Stansted. If you're late getting out of Heathrow and you miss the check-in deadline at Stansted, your ticket will be worthless and you'll have to buy a new one at full fare on a later flight.