vester

Vester, vestra, vestrum is first and second declension and drops its e outside the masculine nominative singular, exactly like noster: vestri, vestro, vestrorum. It is the possessive belonging to vos, so it means "your" when you are addressing more than one person. Tuus covers one. English collapses the two and loses the distinction, which is why a Latin text can be precise about who is being blamed and a translation cannot.

The trap is genitives. Vestrum is both the neuter of this adjective and the partitive genitive of vos, so "unus vestrum" is one of you; vestri is the objective genitive, as in "memor vestri", mindful of you. Neither is the adjective doing its ordinary job, and reading them as possessives produces nonsense.