I had a look at some trees on Ancestry and found a group which includes yours.
Whilst looking for possible details, I found a DNA match with the last one, the Evans-Stephens family.
I can't find the exact link but, according to the obituary of my 3 x great grandfather, Evan Evans, he was born near Bala circa 1775. His parents moved to Pwllheli when he was young and, like your William Evans, he became a well-known Calvanistic preacher in the Caernarfon area.
He may not be related to the Llanycil families on the tree because it also has links to northern Merionethshire and Caernarfonshire areas, where I have ancestors.
I have a number of marriage bonds from Merionethshire and Caernarfonshire, which I obtained from the National Library. None of them mention the abode of the bride, other than the parish. The other signatories don't specify a relationship to the bride or groom but often match names from the family.
I can't see any links to Fedw arian, except for the will of Catherine Lloyd, a widow, in 1733.
Regards,
David