David Ceannt, the grandnephew of Eamonn Ceannt, and Cathal McSwiney Brugha, grandson of Cathal Brugha, unveiled a commemorative plaque at St James's Hospital in Dublin.
The hospital campus, now home to the Trinity Centre for Health Sciences, is the former site of the South Dublin Union.
The SDU workhouse became a focal point in the rebellion when it was captured by Eamonn Ceannt and the 4th Battalion. Former Taoiseach Liam Cosgrave also attended the ceremony.
Mr Cosgrave's father, William T Cosgrave, served in the battalion and played a key role in activities there from Easter Monday 1916.
The unveiling was followed by a performance by St James's Brass and Reed Band.