I couldn't find most of the B rcds for Bridget and her siblings in Co. Leitrim. Perhaps they moved to other counties.
However, I searched for the marriage of John and Bridget Nichols. I found matching M rcds in 1883 for the pair in Cloone parish, Leitrim. These are highly likely to be for your ancestors. A view of the detailed rcds SHOULD reveal whether the marriage was to each other. If so, then the rcd SHOULD also show their parents' names - Thus back another generation.