Archie Miller was much the more prominent player of the brothers. He signed for Hearts from Royal Albert (a junior team) in October 1932, made his first appearance in 1935 and remained with them until 1947. He was capped once for Scotland in 1939 v Wales in November 1938, and once for the Scottish League. He also played after the war for Blackburn Rovers (6 games), Kilmarnock (22 games) and a solitary appearance for Carlisle United. I think he also made an appearance for Falkirk during the war as a guest player. He was later player/manager of Workington.
You will get his career stats on the London Hearts website at
http://www.londonhearts.com/scores/players/millerarchie.htmlGavin Miller joined Hearts in December 1930 but I don't think he played for the first team, joining Dunfermline the following season. I don't have any further info on him.