Hmm, "Llewellyn?" I find that strange in text, myself, but it's a pretty name. Here's something about Welsh pronunciation for you to chew on.
The double L is pronounced by putting your tongue in the regular position for you to make a regular "L" sound, however, you gently blow air out around your tongue instead.
"Ew" is hard to discribe, so I shall rely on a discription I found on a website on Welsh pronounciation.
(The following paragraph is quoted from http://www.britannia.com/wales/language.html
Ew is more difficult to describe. It can be approximated as eh-oo or perhaps as in the word mount. The nearest English sound is found in English midland dialect words such as the Birmingham pronunciation of "you" (yew). Welsh words: mewn (meh-oon or moun); tew (teh -oo)
(End of quotation)
"E" is simply pronounced "eh".
I'm guessing the double L is pronounce as an "aspirated" "L" sound again.
The "Y" is pronounce "uh" because of the "N" consonant at the end.
The "N" is a simply "nn" sound.
So, try to figure out the pronunciation by practicing based on what I told you, or get someone who speaks Welsh to help you out. Welsh is a language with very complicated pronunciations. I wouldn't suggest naming a child this name.