Welcome to Rootschat Nikki
What information do you have on your Robert King apart from what you have detailed above?
I see that the IGI only seems to show one child born to the couple. A Janet King born on 27 Feb 1827 in Old Machar, Aberdeen. HI haven't looked at Scotlands People for children to the couple.
Do you have the couple on census records - and alive after 1855?
The more info you give the more others can help.
Regards, Steve ...
