My Grandmother Mary Kennedy was married from 4 Royal Canal Terrace in 1922 so perhaps she knew Bertie and family.
upon searching for her mother also Mary Kennedy on the 1939 Register of Electors i found what i believe to be her at 4 Phibsborough Road cant find any Royal Canal Terrace 1939.
Similarly i found Sarah Ryan at 8 Phibsborough Road 1939 listed with others same address
Patrick and Agnes Kelly and Patrick Sullivan.
That's right for Sarah. according to my mother she didn't marry but took in orphaned or homeless children. One of them had the name Sullivan. Just like her mother??
Were any of your grandmothers family involved in the war 1920 if so they would indeed have known Bertie. My grandmother was grew up in 188 Phibsborough rd. It was a busy house at that time.