Maud's question seems to have been missed first time around (I assume that Allen's post isn't in answer to it, as Shantalla play an arrangement of a quite different, Scottish form of the song). Two years on is rather late, but since this thread is back from the dead anyway I may as well make a stab at an answer.

Peg and Bobby Clancy would seem possible; they sang a form of the song, All Around the Loney-O, beginning "There were two sisters going to school", which appeared originally(?) on Traditional Songs of Ireland, Olympic OL 6172 (1960s some time; Seamus Ennis also recorded Bobby singing it on his own for the BBC in 1960) and later on various compilations. The Makem website mentions Irish Folk Airs: The Clancy Brothers and Tommy Makem & Their Families (Tradition 2083) and The Clancy Brothers and Tommy Makem with Their Families    (Hallmark CHM 630).

I haven't heard the recording, of course, so I don't know how close it might be to Maud's recollection, or whether it was what she was thinking of at all, but it seems a reasonable starting point. Somebody round here must have it. Comments?