The Fosters and O'Haras are descendents of Robert Bryson, son of James Bryson and Martha Ann McConnell. My Bryson branch didn't intermarry at all. There are no Bryson/Bryson marriages in my line or the lines that came from them for any of my 4th ggf John W Bryson's descendents I think it highly unlikely that I'm wrong about matching DNA to Robert. Those other branches except for John W's brother James have no DNA matches
William Bryson 1869-1938 was one of Robert's sons. Ellen is a daughter but I have her death as 1894. I have a birth record for her as 1871. I don't have any information about any illegitimate children for her.
Robert and Sarah Caldwell had:
James Bryson 1861-1893
Anna Bryson O'Hara 1864-1949 (emigrated with husband Hugh O'Hara)DNA match with her granddaughter as does my cousin
Martha Bryson Gordon b 1866 (both sons from her died on Flanders)
William Bryson listed above
Ellen Bryson listed above
Agnes Bryson Foster 1873-1912 DNA match with her grandson as does my cousin
James never married. There is a PRONI bequest to his brother William.
William had four daughters...Sadie, Lily, Minnie (Matilda) and Aggie. Aggie died at age 6. No death records for Sadie and Lily....surmise they died as infants. Minnie died in 1966. There is no marriage record for her and she's buried in the same plot as Robert and William so I assume she didn't marry.
Robert's daughters had children. As I said my DNA links with the granddaughter of Anna O'Hara as does my cousin and with a Foster of the Agnes line. The Fosters are still in NI.
As I also said there are no Bryson/Bryson marriages in my Bryson line from my 4th ggf to my generation. Those that emigrated didn't marry any Brysons. All the DNA matches I have are from descendents of John W Bryson and his sons and daughters.
I'm very confident about the John W Bryson line. Still looking for a lost daughter but the rest is pretty well documented. Robert is my link to James Bryson and Martha Ann McConnell through his daughters.
Sorry if I sound snippy but I've answered the same questions over and over. Maybe John W will come to me in a dream and give me some hints.

John W had a nephew James b. 1820 d. 1835. He is buried at Kilbride Cemetery.