What happens if two people want to purchase the FTT in any given round?

The player who announced they would buy the FTT does so paying the normal price. If a second person wishes to buy it, taking it away from someone who just bought it, they do so at cost +1 DP. The cost would continue to increase by 1 for each subsequent “steal” in that round.

One notable exception is that Pixies will buy the FTT at whatever the current price is minus 2. No one else benefits from their discount.

Is all of the double-counting correct?

Yes. A turf may be counted up to 3 times:

  1. You control it.
  2. It is the same turn type as your home turf, and
  3. It is used to acquire a rainbow bonus.