Looking for information on John Grannon Co Roscommon & Maria Duffy Co Mayo

Hello I have recently been in contact with a distant relative through a DNA match. He has previously used this message board when he was looking for information on his Great Grandparents Bernard Bryan Grennan and Catherine Callahan (Callaghan) Bellanagare

A previous reply to this message responded with ' your search should include the spelling variations: Grinan; Grinham; Grenan; Grennon; and Gridham.  Bryan & Catherine have 4 children: Mary Margaret Grennan (b. 1865), Peter Grennan (B. 1867), Elizabeth Grennan (B. 1869) and Kate Maria Grennan (b.1872).  

Elizabeth was born on 22 May 1869. Her parents are Bernardo Grennan and Catherina Callaghan of Belangare. The second page of the register shows that Elizabeth was baptized by the Rev. Pat McDonagh on 22 May, which was the day she was born. Her godparents are Joanne (John) Grennan and Brigida Tighe

John & Michael Grennan was Bryan's brothers (see John Grennan of Tully just southwest of Bellanagare)

My GG grandfather John was born in Roscommon around 1854. The only documents I have are census records from England stating his Birthplace and Marriage Certificate 1876 Stoke-on-Trent  to Maria Duffy from Co Mayo. On the Marriage Certificate John's fathers name is Bryan, Maria's father Michael. However I do believe this John Grennan is my GG grandfather as the shared link I have with regards to DNA so far is Elizabeth and Bryan either being John's father or brother. So if anyone is able to confirm if John was Bryans brother. 

Maria was born around 1856 and I have no information as to where she lived in Co Mayo so any insight on this would be amazing.

Apologies for such a long post, but I wanted to share the pieces of the jigsaw I have so far so that I am able to visit soon and be in the right area.

Thank you and Best Wishes   

Bernadette Grannon