"Whose textbooks are these?"
Translation:Чьи это учебники?
You'll certainly be understood, but you'll sound foreign. The Russian analogue of this/these in constructions like "This is/these are X" is always "это" regardless of the gender and number/plurality of X. The same holds for corresponding questions (like this one).
You would use "эти" in statements like "эти учебники старые" (these textbooks are old) and in corresponding questions.