Wish to find out more about my Great Great Grandfather William Reilly

My G/G Grandfather William Reilly/Riley, born 6th May, 1810 at Ballynahinch, County Down and baptised at Ballynahinch by Charles Boyd.   In 1851 he was at Old St, Girvan shown as William Really, aged 37 but would be 41.  His wife was shown as Sarah m/s Brown.  Sarah died in 1855 shown as the daughter of Hugh Brown, Revenue Officer and Mary Brown m/s Darroch. Cause of death was Cholera.  They had been in Girvan for five years.  They had six children.  Elizabeth (15), William (13) , John (11) my Gt Grandfather, Hugh (died at 6 in 1852), Mary Ann (died at 2 years 1949 and Robert (2).  Sarah showed her name as Reillie.

1n 1861 William Reillie was at Girvan, a Cattle Grover.  In 1865 William Rillie married Janet Kelly at Girvan according to the Church of Scotland.  He was a carter.  William's parents are shown as Peter Riely, Schoolmaster (deceased) and Mary Riely m/s Gourlay (deceased).  Strange was that although his father was a teacher, William made his mark.  William died on 10th July, 1890 at Girvan.  Age given by son-in-law as 58 but william would be 80.  The death notice gave father name as John Rillie, Schoolteacher.  my research found a Rev Charles Boyd who was associated with the Church of Ireland in Ballynahinch.  My Great Grandfather had reverted to John Riley when he married in 1867.

Would appreciate any help with regard to Ballynahinch background of William Riley/Reillie or other spellings of his name.