On the 1861 census, Elizabeth gives quite a precise place of birth, as Cefn y Maes, which was an historic farmhouse in Selattyn parish. Richard was born in Rhosygadfa in Whittington (not Rhosgafan in Caernarfonshire as you have in your tree!). So I would assume that a marriage would have take place at St Mary's parish church in Selattyn or, at least, nearby?
Baptisms at St Mary's parish church, Selattyn:
Andrew Myatt was baptised on 14 Dec 1828, s/o Richard Myatt & Elizabeth
Cathrine Myatt was baptised on 1 Aug 1836 d/o Richard Myatt & Elizabeth
Edward Myatt was baptised 5 Dec 1831 s/o Richard Myatt & Elizabeth
Baptisms in Oswestry:
Thomas MYETT was baptised on 1 Apr 1827, s/o Richard Myett & Elizabeth
Where did you get the "Bennett" surname? I think it may be wrong?
I think it comes from a marriage for a Richard Myatt and Elizabeth Bennett in Audley, Staffordshire, England in 1824. On Ancestry, some people have attached this marriage to the Selattyn family, but Audley is a long way from Selattyn and the censuses show that the Staffordshire Myatt's remained in Staffordshire!
There is a marriage for a Richard MYETT and an Elizabeth Jones on 17 Jul 1826 in Oswestry. I suspect this is the one you are looking for???
Also I suspect that this could be Richard's baptism at St. John the Baptist parish church, Whittington:
30 Oct 1796, Richard MATE, s/o Richard Mate & Margaret of Ebnal.