seems like the same marriage to me - other than the bride's name it's far too much of a coincidence for it not to be. (same date, same groom, same bride's surname, same witnesses, same general area...)
Maybe it's possible that there was a mixup either submitting the civil record at the time, or the IFHF record transcript has some names mixed up for that section of the register...
I had a quick look at the BMD index and only see one Patrick Duffy marriage in Roscommon in 1868.
Can you not confirm the bride's name by checking birth cert details for their children ?
I'm not very familiar with Roscommon townlands and parishes but could Kilbride be the name of the parish and Kilgefin the name of the church or townland where it's located ?
dont know where you are based but another option might be to check the actual register film in the National Library.
Shane