There are a lot of Sean O Tuamas out there!

According to ainm.ie, Seán Fear Ó Tuama, the father of Seán Óg, has dates of 1882-1972, and was interned more than once between 1920 and 1925. With his wife, Síle Ní Mhurchú, he had five children. I can identify three of the five. They are obviously Seán Óg, the musician; Máire; and Séamus. The last of the three, Séamus, was an actor with a day job (civil service), who married Róisín Ní Shé the singer and harp player. Eamonn de Barra, featured several posts back in a linked video, is their grandson. So, as someone surmised earlier, there is a blood relation.

The ainm.ie biography entry (in Gaelic) says that Seán Óg's mother Síle had a great repertoire of songs, and from her, he learned songs in both Gaelic and English.