It just doesn't all add up yet

No suitable Samuel Palmer birth 1865-1878 in GRONI's database (covers all 6 N.I. counties)
No suitable marriage for a Samuel or John Palmer with wife Margaret in N.I.
So, a few questions which might help us find the family in Ireland...
1) what's listed for birthplaces of Samuel Palmer, his mother Margaret Jane and brother John? Often that census is the one which lists a more exact place of birth than 'Ireland'
2)
I managed to find margaret Janes death certificate. And that says her husband was a John Palmer??? Her mother was called Mary Harvey. Father's name? Margaret's age? who was the informant?
3) have you searched for the family in 1891 Scottish census?
4) numerous online family trees give Samuel's mother as Margaret Ann. They could be mistaken, copied from each other, etc. but have you tried contacting others interested in the family?