The family broke apart due to the death of Robert and Elizabeth (the parents) both in 1872. The 2 youngest daughters went into the Ballacloan House, the next youngest was John James who likely moved to the 1881 household you detailed. He is actually the nephew of Isabella Moughtin nee Kinley, not a Boarder. All of the older children moved onward elsewhere.
My concern is still the "death" of John James reported on April 2, 1866 as reported in the IGI when there clearly is a John James alive with no evidence of another child with the same name for these parents.
Sally