It has taken a while but I now think I know whose Thomas' father. He was illegitimate, as was his son Alexander Powrie.Thomas' father was a wealthy merchant and shipowner named Thomas powrie (born about 1779-1847).
Thomas Powrie was married to the daughter Juliana Glover, of his Theatre Manager of the Theatre were Thomas was an actor (Samuel Edmond Glover)They were a family of famous Theatre people. For instance Juliana's brother was the premier theatre set painter in Scotland.
Thomas had no children with Juliana, but had a child out of wedlock with a 16 year old domestic servant Mary Nicholl (1832-1856), named Alexander Powrie. Mary's parents were William Nicoll and Ann Hume.
I have a film of Thomas Powrie's prompt copy of Hamlet, which has Thomas' notes, and ideas for stage placement of actors and drawings of Costume ideas. Obviously, he was interested in managing a play, not just acting.