Burnash Hill is fine for Martletwy.
William Picton a collier mrd Sarah Watkins at Martletwy 29 Jan 1831.
I suspect William is related to the Widow Margaret Picton who is living down the road at Westfield in 1861, she was probably mrd to John Picton who mrd Margaret Cole at Martletwy 03 Mar 1827.
Whilst William may be the son of John Picton who mrd Elizabeth Davies at Martletwy in 1777 I'm not so sure and would even question whether William was born/baptised at Martletwy as he and Sarah claim in 1861, I would be looking more to the West for his baptism entry.
Its a pity the Picton wills of the ECC of St David's do not offer more than they appear to.
I note you have 'circa' for the childrens baptism, if you search the IGI for all Picton's in Wales you will find most if not all the baptism's you require to Wm & Sarah at Martletwy.
Rgds
Orielbenfro
ORIEL a welsh window on a surname