That birth year of 1841 seems to come from his death record?
The grandson James who was the informant seems to have been the son of John and Mary (Kehoe) Copeland, who married in 1894 at Ballymorris. They appear with John's parents John and Mary Copeland at Ballymorris in the 1901 census. In the 1911 census, John and Mary appear alone. Those census records indicate John was in 1734 or 1736. So there appears to be uncertainty about his birth year.
His wife Mary's death record shows her born around 1838, the informant being her son George:
John and Mary (Morgan) Copeland recorded several children from 1864 until 1880, fitting with Mary's birth year around 1838 and a marriage around 1863.
Unfortunately, I don't see a marriage certificate for John and Mary, even though this is in the time period after civil registration of marriages started. The certificate would show his parents. If you can track it down, that may be just what you need.
There don't seem to have been a lot of Copelands in that region, so your hypothesis that John and Robert were related seems to me a good one to pursue.