Is it permissible to marry the mother of one’s stepfather’s second wife, and what is the Shar‘i (Islamically lawful) term for the mother of the wife, along with the proof?

It is not forbidden for a man to marry his paternal wife's mother, because there is no text prohibiting it, and because she is not among the women forbidden in the Qur’an and Sunnah. The scholars have stated this.