E.L.
Would you pronounce Thyler like Tyler? If you pronounce the th, it would sound like a lisp. I like Tevin on its own, but personally, I don't like 2 kids to have names that sound too close (just wait until they are teenagers and you can't tell which kid someone is calling for on the phone!). Taten and Tevin are similar not only in the first vowel sound but also the last syllable.