Who is Coll MacGregor from Rebellion and what is their importance?

Coll MacGregor is Serena's brother. He and Brigham Langston are good friends. When the two travel to Scotland to prepare for battle against the British, Coll is injured when they are attacked by hated Campbell clan. When Brigham gets him home and into the house, he sees Maggie MacDonald and is immediately smitten. Coll later proposes and the couple marry. In the end, Coll, Maggie and their baby stay in Scotland with Fiona MacGregor, while the Langstons and young Malcolm leave for the New World.