Flamers must be deployed at the same time and within 5" of the unit of Horrors they have been bought with. After that they are free to move as they like, and each counts as a separate unit for the rest of the game (including for the purpose of calculating Victory points). If a Flamer is more than 5" away from a unit of Horrors at the end of any Chaos turn, it must immediately take a Leadership test. If the test is failed, the daemon is destroyed.