@MereDintofPandiculation , the w in Betws is like a very short oo. Like the o in to but not long like the oo in too. If you hear to and too as exactly the same, I can't help you. Cwm is pronounced like 'Come' in a mock yorkshire accent and not like Coom/Combe
If you say Betsy Coyd, they'll know where you mean 
I think Ll is similar to lch in German, which isn't like l followed by scottish ch. I'd say german milch as meLL
U - no equivalent. The tongue makes a horseshoe shape. In S Wales it sounds more like i (very short ee or i)
Two vowels next to each other form diphthongs and many have no equivalents. There are english sounds that you can't write in welsh and the other way round.
Ten and Kitten sound different because one becomes a schwa. If the words were welsh Kitten would be KIT-enn, not Kitt-n
You get welsh women called Helen - and they say it as HELL-enn not Hellun or Hellin. Elen is ELL-enn not Ellun
As I pp, the arguments on the 'welsh' threads are usually between Welsh-speakers and non-Welsh speakers, who will argue with you that Mair is pronounced My-uh because they know someone from Fishguard who says it that way, or that (non-Welsh speaker) Dylan Thomas said his name as Dillun. Part of the reason I kicked off on here is because of the stereotyping on TA. I'm not sure how much Welsh the Caitlin actress can speak, but she sounds very welsh because she's from Port Talbot. She was on a tv show about 10 years ago and said she couldn't speak it then. Mispronouncing a popular name should not have happened. It's as basic as getting William wrong. She wouldn't have referred to herself as Grandma. She turned up with welsh cakes, they had a cwtsh and a sing song and excluded someone in conversation.
I mind that british-pakistani Adil has a british-indian accent and that they say his name as Ardil, but it doesn't quite grate in the same way. It strikes me as ignorant, but it doesn't offend me like the welsh stereotyping does.
Tom should have taken Natsha's surname when they got married