Kew is that the same as the Cein in Ceiniog (penny) - sounds like next of...kin.
Dh is from Anglesey, so we would go with the north wales pronunciation if different, but he doesn't know anyone called Ceinwen - which is why I am checking.
BTW, DD1s middle name is Bronwen - and I have often regretted not keeping it for a first name! It's a gorgeous name - but I agree, definately has to be pronounced as 'wEn'
It's going to be a middle name, so I'm not worried about people not being able to pronounce. Will have more 'standard' name for first name.