they had 4 children Sarah Isabella Alexander 
Who was the fourth child and when were they all born
Do you have a copy of their marriage cert showing James' fathers name and occupation?
Marriages June qtr 1857 
James Patton         Alnwick    10b   384     
Isabella Rogerson    
EDITNot sure that is the correct marriage as 1861/1871 for Alnwick does not show children mentioned in post and shows James as b Northumberland