a serious question, how do you handle those sorts of "relationships" in your family tree? 
Hi
Mary Ellen Williams was the mother of Agnes Williams. Her parents were Alexander Plunkett, stevedore, and Susannah McLuskey
James Plunkett married Agnes Williams. His parents , on the marriage cert, were Alexander Plunkett, stevedore and Susan McLuskey.
Thus James was Agnes's full uncle - so Agnes gives her mother's MS as Rooney. Even if Mary Ellen was a Rooney (good name

), he would be Agnes's half/step uncle

I don't think it was legal to marry one's niece in 1904 - not in England anyway

gnu