Welcome to Rootschat!
I guess you know what I'm going to say - you need to get that marriage cert when you can. If it was later in the century, you might find an earlier census, but the couple are already married by 1841. Your other problem is that your man is a Baptist minister. This suggests he may have been born into a Baptist family, so you wont find an infant baptism for him as Baptists don't practice that rite. He may have been baptised around the age of 15 & any surviving register may not mention his parents.
http://www.baptist.org.uk/believers-baptism/what-is-baptism.htmlHave you followed the couple & their children through the census years? I can see that Rachel died between 1851 & 1861 and John remarried to a Hannah.
death reg?
Rachel Michael march qtr 1852 Chepstow vol 11a pg 3
possible remarriage
John Michael dec qtr 1853 Pontypool vol 11a pg 261 with Hannah Davey on the same page
In 1861, John & Rachel's daughter Margaret is with relatives, so that looks to be Rachel's family
Cwmmera (?), Llantilio Crossenny
William Jones head widower 80 farmer of 123 acres employing 1 labourer & 2 boys b. Llanwenarth
Benjamin son unm 41 b. Llanwenarth
Eunice dau unm 36 b. Llanwenarth
Mary dau unm 29 b. Llantilio Crossenny
William Charles Taylor visitor 24 student Baptist College b. Somerset, Bishop Lydeard
Margaret Michael niece 12 b. Llangwm
Sabina Jones 17 house servant b. Abergavenny
Cornelius Pritchard 20 carter b. Llantilio Crosenny
John Davies 13 general servant b. Llanvetherine
I suspect that niece here is used in the old fashioned sense of female relative of a younger generation and we would say grand daughter instead. I'm not finding parish baptisms for this family, so they could also be non-conformists. Finding the other children in 1861 may help with other family members.