See where you are going Sancti...and where Harry has already been!
Likely the transcript has son John as 71 rather than 7

JOHN DEVLIN Birth: 06 SEP 1863 Whitburn, West Lothian
Parents: JAMES DEVLIN and BRIDGET REILLY
Harry, the 1855 birth cert for Hugh will at least hopefully provide some clues on parents's origins and marriage date. You have their death entries already from what you have said

Monica