Hi Donna,
The Robert who married Agnes DALZEL [DANSELL/DUNSELL/DAUNSELL/DUNGELL/DUNZEL/WANSELL] 31 July 1847 Kirk German can't be the Robert who was still with his parents (Thomas & Margaret) in the 1851 census you posted.
According to the 1861 census he was also born in Maughold (c.1825) amongst the other numerous Christian families.
Possibly the son of the Mark Christian/Margaret Kissack bapt 1 Aug 1824 who you noted.
Sue