Excel and Air Atlanta Europe are supposedly eventually merging to become one, although Air Atlanta Icelandic will remain separate. Travel City Direct are not an airline they are a tour operator to Florida. They just charter the flights to Sanford, and part of the agreement is to brand them in TCD colours. Travel City are like Cosmos, Airtours, Direct holidays etc.
Interesting though that the Avion group have acquired them. I assume the TCD brand will be kept on as its quite popular, guess this move ensures Air Atlanta keep the lucrative Sanford flights in the future.