Family search: Mulroy/Jennings

Hello, We have been looking for the family of James Jennings (born c.1800) and Nancy Mulroy (born c. 1805), who married around 1827 in Co Mayo. We know they were from Co Mayo and emigrated to America around 1840. Their first three children were born in Ireland (Mary c.1828, David c. 1836, and Thomas J. c.1839). I have searched for neighbouring townlands with these names and have found Jennings in Gortaphuill and Mulroy in Rathnacreva in Rosslee parish. I have also seen these names in Islandeady parish in townlands which are not far from each other. But I haven't found the names of James Jennings and Nancy Mulroy or their children. For some reason, the Rosslee parish isn't even on the RootsIreland site. Do you have any suggestions about this? Thank you very much for your help.