"Dych chi'n hoffi Owen?"
Translation:Do you like Owen?
Not entirely correct as yn comes before a verbnoun, not a verb.
The usual sentence pattern here is:
verb + pronoun + yn + verbnoun
Dych chi'n hoffi/mynd/helpu... (Do you like/go/help...)
Eisiau is/was originally a noun that used another construction, but ended up being used in the same part of a sentence as a verbnoun. The fact that it was originally a noun means although we use it like a verbnoun, we still don't use yn before it.
verb + pronoun + eisiau
Dych chi eisiau... (Do you want...)
It's just a weird one, so you just learn it really.