Not sure I have anything that will help you at this point, but just posting in case we can compare notes in the future.
My 2x-great-grandmother was Margaret Guinan, who married Joseph Farrell and lived in Endrim. That is just north of Ferbane, which is east of Shannonbridge. I have not gotten far at all with the Guinans - even with the help of local cousins who research.
(My Gran May Egan was her granddaughter and was living with her in the 1901 census. The rest of the Egans were living nearby in Creggan.)
My Gran and later 2 sisters emigrated to NY. One of the sisters married a James Coffey here. I have not researched the Coffeys at all, but when going through photos with a cousin from Ireland she pointed him out in one of the group family photos in Creggan, so I assume he and his came from around there as well. I'll have to check with the cousins though to make sure he wasn't just visiting with my great aunt.
My great-aunt Rose Egan also married a Michael Kenny and the family owned the Cosy Bar in Ferbane for many years. Haven't researched them either, though.
If you would like to compare any notes or info, you can reach me through Ancestry messaging or via my blog's contact page:http://currach.johnjtierney.com/contact/
(Don't like to post email addresses in forums.)