Hi Jenn and Lauren
The marriage was 1848 Jenn - before civil registration - little information.
I found this information on the IGI, it might be the family
John Campbell married Janet MacDonald 16 FEB 1827 Latheron, Caithness, Scotland
which is where the family were living on the 1841 Census
Helen baptised 4 Oct 1829 Latheron
Christian (female) born 29 May 1831 baptised 5 Jun 1831 latheron
Elizabeth born & baptised 13 Feb 1833 Latheron
all have parents John Campbell and Janet McDonald
These three tie in with 3 of the children in 1841 - Helen 11, Christina 9 and Eliza 7
It is possible Margaret was born before the marriage?
Also on the IGI baptism Margaret Campbell 8 Nov 1822 Latheron, father John (Mother's name is not given on these early dates in Latheron). Given the rounding of age in 1841, this could be daughter Margaret.
I don't easily see the youngest two born in Caithness. There is a Jane of the right age wrong parents
Trish