Here's the official announcement via their Facebook page:
Aislin McGuckin has been cast as Letitia MacKenzie, the wife of Clan MacKenzie's Laird Colum MacKenzie and mother to Hamish. As the spouse of the most powerful member of the clan, Letitia plays the role of both matriarch and caring mother. A strong woman in her own right - the type of powerful ally Claire, or anyone, would love to have.Next we have Liam Carney who will play Old Alec.
Below is STARZ's official announcement:
Liam Carney will play Alec McMahon MacKenzie aka Old Alec. This squat, powerful man is the “Master of Horse” at Castle Leoch. He serves as a boss and in a way a mentor to Jamie at the stables. A bit gruff, he is definitely a man’s man.All in all its other great news in the world of Outlander!