Yes I believe Hal Holbrook is related to the Myers family and also to Francis Preston Blair. Hal played Francis Preston Blair in the new movie Lincoln.
The Myers Preston Blair Breckinridge Carter families are all intermixed and connected to the Myers Iron Works in Kentucky. They would also be connected to the very first Nickeloden in the world located at 433 Smithfield Street in Pittsburgh built in 1905.
Francis Preston Blair nominated General John C Fremont for the Rebublican Ticket at the Pittsburgh Rebublican Convention in Feb 1856. That didn't hold so James Buchanan won. His Vice President was John Cabel Breckinridge.
James Buchanan's brother was married to song writer Stephen Fosters Sisiter.
Many of these families were connected to Union Major Martin R Delaney who was a close friend of Frederick Douglass and his business partner Issac Myers from Baltimore.