Thanks for this Gaynor, Sorry I didn't recognise you as a previous contact. The tree is many branched and I make the fatal error of trying to deal with many branches at the same time; with obvious complications!
Is the marriage you have in Capel Garmon 17/6/1837 that of "your" Evan (son of John & Margaret;I believe)? If so then maybe the marriage I found (to Catherine Williams in Capel Garmon ) is for "my" Evan (son of Lewis and Dorothy). The fact that he was a widower makes a bit of sense in that there is a son (William) to "my" Evan who was born before that marriage.
Is "your" Evan's granddaughter Mary Ellen Morris the daughter of Cadwaladr Morris? i.e. did Margaret Roberts marry Cadwaladr Morris? The censuses of 1901 and 1911 give Richard & Mary Davies living in Blaenau Ffestiniog along with Cadwaladr. The latter was born in Rhydlydan near Pentrefoelas.
I have just realised that this info may have come from you in the first place... oops. Sorry. I am very disorganised.
I'd love to have any details and photos you have. I'll send my e-mail address in a personal link.
Best wishes & Happy 2013