Who was Margaret C. O'Neill Brennan?

I started this post as somewhat of an electronic worksheet.  A DNA relative on Ancestry.com had a tree that showed some ancestors Nicholas T. Brennan and "Margaret Ella".  There was little information about them but one thing was clear, they lived in Baltimore.  Although I could not know for sure which branch of the Ancestry member's family I was related to, I thought this was the best place to look as my family goes back five generations in Baltimore.

From the list of DNA relatives that we shared, I knew that the member was connected through my McGovern / Dixon branch and she was estimated to be my 4th to 6th cousin.

It took three hard days of work but eventually, I was able to build this tree around Margaret and Nicholas:

nc - no children

nm - never married

c - had children but not named here for confidentiality reasons

SMG - St. Mary's Govans Cemetery

NCC - New Cathedral Cemetery

BNC - Baltimore National Cemetery

SAE - Saint Augustine's Elkridge Cemetery

Some of the pieces of evidence to prove the family, with notes from when I found them)  include:

This is the index card from the Maryland State Archives where wedding licenses and weddings were recorded.

This is the 1900 census form showing Margaret O'Neill and Nicholas Thomas Brennan family.  Note the last name in the home: Jane O'Neil, born in August 1823 in Ireland.  She was listed as "mother" but it is most likely Margaret's mother, rather than Nicholas'.

This is the obituary for Margaret C. O'Neill Brennan who died on 29 September 1911 in Baltimore.  Note that she has a sister named Ella O'Neill.

Nicholas Thomas Brennan appears to have died in Baltimore around early August, 1939.

Interestingly, Nicholas appears to have married again after Margaret died.  I am willing to bet you a dollar to a hole in a donut that his second wife was Margaret's sister, Ella, based on the following obituary:

The sister shown as "Mrs. Christopher Maddox" in Margaret's obituary was Catherine Alice O'Neill (12/1862 Md. - 9/26/1934 Md.).  Christopher died on 2/22/1907 in Baltimore and is buried with his wife in New Cathedral Cemetery.  They had three sons, only one of whom appeared to have married.

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The obituary of the mother of the three girls leads me to believe that she is the link to my family.  My great-great-grandmother was Catherine Dixon, the sister of Joseph Dixon, the prelate of Ireland.  I knew from Joseph's biography that their mother's name was Jane Casey and that they also had a sister named Jane.  This sister though was born about 1815 and she had married James Magill and stayed in County Tyrone, Ireland when her sister Catherine came to the US.  Based on the name and date of birth, I suspect that Jane Dixon O'Neill  is most likely a cousin of my great-great-grand mother Catherine Dixon.  That would make the Ancestry member my fifth cousin.

The obituary of the father of the three girls was easier to find after finding Jane's.

One surprise popped up while I was looking for the father though.  Margaret, Catherine and Ella had an older brother that died, unmarried, many years before the girls did.