Looking for Family of Peter Omalley M Margaret Riodan

I Have a Certificate that says They were parents of my grandmother who I never met.I have asked a few elders who are left but I seem to run into road blocks cause of hard feelings which must of been a big thing back in the day.Anyway I dont care I am trying to build a family tree here and Tim McCarthy and Ellen Ferry were my grandpas parents and Peter OMalley and Margaret Riordan were my granmothers parents.If any one could help me I would be very Thankful.