Hi Jackie,
You omitted to mention the name of the famous Irish Showband so I did a bit of googling as I'm interested in the Showbands that toured Ireland.
Lala Harden and the Slieve Foy Irish Showband is a new name to me.
The post War Showbands are well documented but it tends to be difficult to get information about the earlier bands. I think there may well be a reasonable amount of info if you're able to get to one of the Newpaper Libraries in Ireland and have a hunt through the papers which were published in the area in which the band was based.
I don't know if this has any bearing on the subject but Slieve Foy (Irish: Sliabh Feá), or Carlingford Mountain, is a mountain that rises near the town of Carlingford, County Louth. I tried thecore.com/seanruad IreAtlas hoping there might be a townland called Slieve Foy but nothing appeared so it still looks as though there's a Co. Louth connection. Brennan was a common name in Co. Louth at the time of Griffith's Valuation in the county in 1854. You have Lala Harden in Co. Donegal a hundred years later.
The Clannad website mentions Moya (Máire) Brennan who was a niece of twins Noel & Padraig Duggan, from Gweedore, Co Donegal, who played in the new Slieve Foy group. It seems I'm on the right track ... I've found another of your messages about the Brennan family ...
Brennan. Harden. Sleive Foy .Leo Brennan . Clannad., Enya and Defrench on RootsWeb.com
You've made no mention of Mena's surname so the information in Irish Anscestors Surname Search is not too helpful ... Brennans and Hardens appeared the same parish in the following counties between 1848-64 ... Armagh, Cavan, Cork, Cork city, Dublin, Dublin city, Fermanagh, Kilkenny, Laois, Offaly, Tipperary, Tyrone and Waterford. On the information that you have about the Brennan family of Clannad I feel that your Brennan ancestors probably came from one of the northern counties.
Christopher