Tracking John Chapman appears to be relatively simply if the one I've found is the son of Charles and Mary Wood.
The LDS Church index has his birth as 14 April 1810 in Fetteresso
In 1841 he is in Fetteresso, married with 3 children plus two possible siblings in the household.
By 1851 he has moved to Midlothian (Edinburgh) with 6 children in the house.
No sign of him in 1861.
If this is your John then not only would Robina be illegitimate but John would have committed adultery.
However, there is another John Chapman who muddies the waters. His birth is shown on the LDS Index as 25 October 1823 to Morris Chapman and Jean Merchant. He would be old enough to have fathered a child in 1844. He is in Fetteresso in both 1851 & 1861.