Hi Agnes
Welcome to RootsChat

Just a couple of suggestions that might help you with further info.
I assume you have their marriage year and place from one of their children's birth certs. If you haven't already, it certainly worth looking at the birth reg of their daughter Agnes (b. 29 December 1855 BO'NES). Surname on the index spelt Mildoon. The first year of official registration in Scotland and BMDs ran over two pages of the register for one year, with lots of additonal info. For birth certs, it should include date and place of marriage (which you have), normally includes age and birth place of parents, how many children they had (alive/deceased, girls/boys).
If they followed naming pattern for their children (the Scottish and Irish often did in some form, see for example
www.halmyre.abel.co.uk/Family/naming.htm) it is worth looking at the names of their children for possible clues to grandparents' names. All birth looks to be in Bo'ness:
Patrick born 1850 (from 1851 census)
John b. 1852
Catherine b. 1854
Agnes/Anne b. 1855...Agnes in birth reg and Anne in christening
Mary b. 1857
John b. 1859...Likely first John died?
Margaret b. 1861
Peter b. 1863....the name is a common variant of Patrick. Did first Patrick die?
Charles b. 1864
Mary b. 1866...Likely first Mary died?
James b. 1868
Mary Ann b. 1870
Important family names were often repeated following the death of a child with that name.
There are three RC christenings for John, Catherine and Anne on the Scotlands People's RC registers. If you haven't already, might be worth checking to see whether any family surnames show as godparents.
Monica