United States Senator John J Crittenden of Kentucky had two sons that served in the Civil War but on opposite sides. His eldest George Crittenden started the war as a colonel in the Confederate Army and had been promoted to brigadier general and major general. Yet he was later demoted back to colonel after charges of drunkenness. Thomas Crittenden started the war as a brigadier general in the Union army and was later promoted to major general.
American Civil War page