αὐτῶν [86 verses](pron/adj pl masc/fem/neut gen) "Their" is auton, is the genitive case of the third-person, plural adjective that is used as a pronoun. The word also means "the same," "one's true self," and "the soul" as opposed to the body. It also means "of one's own accord." -- The word translated as "their" is the Greek adjective that acts like our third-person pronoun. The form is the third person, plural in the genitive form. It is used as a possessive or the object of a verb or preposition.  As a preposition's object means a movement away from something or a position away from something else. This pronoun follows the noun so "of theirs."