John Cashin married Mary Coffee 30 May 1835 in Patrick.
He and brother William appear to be the children of John Cassin and Eleanor Clark
She, Mary appears to be the daughter of Daniel Coffee and Nora Sullivan and born in Killarney Kerry 1802
In 1851 they lived with children in Shore Road Peel although Mary's name has changed to Margaret the children remain the same :-

Margaret 16
Mary 12
John 8
James 5
Robert 3
Elizabeth Jane 3m
Thomas 3m

William came later in 1853, there was another John who died after 8 weeks in 1842 and Robert may have died in 1866 age 18.
Also in Shore Road was John Coffee and family. He was the brother of Mary (Margaret?)
By 1881 William 1853 was living with Margaret and son in Love Lane Peel and fishing from boat 'Auspicious' together with Edward Fargher, William Clarke, John Burden and James Hughes- he matches Margaret's brother.
James Hughes (the father) and wife Elizabeth Collister also lived in Shore Road with family. He is listed as from Ireland.

You need to check some of the early comments

Len Faragher