Family mystery

Hello all.

I have been researching my family tree and history of late and have been quite successful, especially with my North American roots. However my mother's paternal side is proving to be quite the challenge. I have a family mystery that I cannot solve, and it comes from some family folklore that has been passed through the generations. I was hoping maybe someone on here could offer some advice.

My mother's father always spoke of a French connection. He was born and reared in Tullyvin/Drumnagran, outside Cootehill. His mother is said to have been fathered by a Frenchman, who, so the story goes, worked for the Coote family at Bellamont House. His surname is thought to be a variation of Denoir. My grandfather's mother is listed variously (on her children's birth registrations, civil and church) as: Mary Denoir, Denipher, Denivor, Devine, and Denvier. On some she is also named as Brady, because her mother's second husband was a Brady. The Frenchman, Mary's biological father, was said to have died, allowing her mother to re-marry. The story goes that the Frenchman was employed by the Cootes at Bellamont House in some capacity, possibly as a tutor to children. Mary's mother may also have worked there, and is where they are said to have met.

I have photocopies of all Mary's children's birth registrations, both church and civil, and also the marriage certificate for Mary Brady & James Smith.

I should also make you aware that I have been in touch with a descendant of the Bellamont House Cootes (and current owner) and he has no family documents that might shed light on the story, unfortunately.

Also: this may be a red herring, but Mary Denoir's mother was said to be Scottish, named McDonald (her maiden name).

Any ideas on what my next move might be?