Is that your Martin marrying a Margaret Doyle in St. Andrew's RC Dublin City in July 1878 ?
The parish record notes the fathers to both Martin and Margaret are shown as deceased, residence for the mothers as Aghowle for Mary Kenny, and Shillelagh for Mary Doyle (no maiden surnames recorded for the mothers). The marriage cert (civil record) has ommited occupations for the groom and both fathers.
Have you located Martin and Margaret on the 1901 and 1911 census ?
I dont see any sign of a promising match for Martin's baptism in the Catholic records available. Have you come across any possible siblings to Martin, e.g. as godparents to his children etc ? It might be worth a closer look through the register images for the parish on the National Library of Ireland website to see if his baptism might have been mistranscribed. Most of the parishes in this area have records back to the 1830s at least, and a few back to the 1700s.
Crab Lane Crossroads is shown on the c1840 OSI maps and covered parts of about three townlands Aghowle Lower, Coolkenny and Barnacahsel, all in Aghowle civil parish, which was part of Clonmore Catholic Parish, the parish covered parts of Counties Wicklow and Carlow. Baptism records for this parish are available back to 1819, so if your Martin was baptised in the parish you would expect him to be included. The records look legible and fairly complete for the late 1840s/early 1850s. The placename on the marriage would be the current residence for the parents, in this case just Mary Kenny (nee unknown) - maybe that's not where the family lived at the time of Martin's birth...
When the older civil death registers are added online it might be worth checking for possible matches for Matthew Kenny - although I dond see anything promising on the index, hopefully he died 1864 or later...
There are a number of possible deaths for Mary Kenny after 1878 in the right area Shillelagh district, but have not located a good match so far. If a death for her could be located r.g. a widow in or near Crab Lane Cross Roads, it might help if the informant is a family member, e.g. a son or daughter