As you probably know, people tend to say "Dilan" in English. Welsh y only has that sound when it appears in the last syllable of a word. Like gwynt or Dilys. Elsewhere it's kind of like the 'u' in "cup" (identical if you have a Welsh accent). Hence why it sounds like "Dull-un". You hear it both ways in yfory - "uvvory".

For people without a Welsh accent, the 'cup' sound is pretty close, but the sound most people have in unstressed syllables is identical - like the 'o' in "today" or the 'ai' in "mountain". The linguistic name for that sound is "schwa": ə.

It's an untranslatable grammatical particle used with a verb in the present tense. This sentence is word-for-word "am I not yn liking Dylan". When yn follows a word ending in a vowel, it gets shortened to 'n. dw i'n (I am) vs. dw i ddim yn (I am not).

It's unrelated to the other yn, which means "in", and can be told apart from context. https://en.wiktionary.org/wiki/yn#Welsh

Eisiau (want) and anghen (need) are nouns rather than verbs, so they don't take yn. Dw i eisau - "I am [with] desire".