Thank you for the link, it is very interesting.
I had found the family of Thaddeus O'Dowda and and Ellen White in "The Genealogies, Tribes, and Customs of Hy-Fiachrach : Commonly Called O'Dowda's Country", but I wanted to be certain that the David who married Emma Sidney and Thaddeus, one of the witnesses, were brothers, as seems possible or even probable. I know James Vippler would be another brother if this were the case and this would open up a whole new area.
Thanks again for your help.
craggagh.