Why is "é de você?" not acceptable? "É de vocês" is, why not the former?
Is "E o seu" acceptable as a translation here as well?
I think "o" is an article like "the" so it is not acceptable
If you and your friend have one black cat each. You can point to one of them and ask "é o seu?".
The "o" there helps on the identification of the specific cat (it could be anything, not just cats).
But in general, you can omit the article.
Why is teus not accepted?
Teus is plural, it is singular. É teu worked for me.