For John McHugh B 1848 +/- 1 yr, Co. Leitrim, with the father's forename unknown, I found 2 rcds: 1847 Kinlough RC and 1849 Kinlough RD parish/districts. Father's respective forenames were Patrick and Michael.
I didn't see any matching M rcds for John and Mary in Co. Sligo. There are POTENTIALLY matching rcds for them in the range 1876-1884 in Leitrim. Will leave it to you to find if there are matching rcds at the parish level of detail.