Welcome to Ireland Reaching Out!
I searched the subscription site Roots Ireland and the only John Holmes/Margaret Mangan marriage was in 1835 in Manister (also Fedamore) RC parish.
John Holmes may have been from Kilfinance but that parish is a good deal south of Manister/Fedamore. I did not find any children for this couple on Roots Ireland.
Date of Marriage:03-Jan-1835
Parish / District:MANISTER
Husband John Holmes
Witness 1 James Holmes
Witness 2 TimothyManagan