Patrick Glynn/Margaret Shea and James O'Neil/Mary Unknown, Co. Galway

I am hoping someone can help me establish a definitive connection between Patrick Glynn/Margaret Shea from Co. Galway and James O’Neil/Mary Unknown (also, I believe) from Co. Galway. 

James O’Neil and Mary Unknown were my gr-gr-gr-grandparents (no dates available but born probably around 1800).  Their daughter Mary O’Neil (approx. 1828-1889) married Thomas Dolan (approx. 1807-1867) (both I believe from Co. Galway), and they had a daughter Margaret Dolan (born in Liverpool on July 4, 1848 or 1849). In the 1860’s, Mary (O’Neil) Dolan and her daughter Margaret came to America.  In 1869, Margaret, a young widow, married Joseph Martin Bonning (from Prussia) in Boston.  The U.S. Federal Censuses for 1910, 1920, and 1930 list Michael Glynn, a bachelor cousin, living in the Bonning household in Malden, Massachusetts.  Other family trees on Ancestry.com show Michael Glynn, list his birthdate as December 24, 1836, and his origin as Ryehill, Co. Galway (I have been unable to verify this information—he may have been born as late is 1839, according to his naturalization papers).  His parents, according to an affidavit signed by him in 1909, were Patrick Glynn and Margaret Shea from Co. Galway.  Again, according to other family trees, he had the following siblings born in Co. Galway:  Edward J. (born 1840), Nicholas (born 1845), and Ellen (born 1846).  I have several DNA matches with descendants of Edward J. Glynn, and I suspect that my gr-gr-gr-grandmother Mary (maiden name unknown) was born Mary Shea and that she was Margaret (Shea) Glynn’s sister, but I lack documentary evidence.  I am hoping that perhaps there is a baptismal record or two available that would show Mary Shea or James O’Neil as a godparent for one of the Glynn children – or some other documentation available that would substantiate my belief.  Many thanks in advance for any help!