It is possible that John and Margaret left from Co. Cork but were actually residents of another county. I had searched two sites: subscription site Roots Ireland and the free site www.irishgenealogy.ie for Co. Cork baptismal records and only found one record for a Margaret Lawlor with father John. The details are below. However, I did not find baptismal records for any siblings of this Margaret Lawlor including a John..
Margaret Lawlor baptized June 22 1856 Youghal RC parish father John Lawlor mother Mary Baker
Are you aware of the names of any other siblings. Have you located the death record for Margaret which might show her mother's maiden name?
Have you considered a DNA test which might give you matches on your Lawlor line?