Is the husband's granddaughter's son considered a mahram to the second wife?

The wife of the maternal grandfather is considered a mahram, based on the words of Allah the Almighty: (And do not marry those [women] whom your fathers married, except what has already occurred. Indeed, it was an immorality and hateful [to Allah] and was a terrible way.) And Malik mentioned in Al-Mudawwana: "So, what the maternal grandfather married is not permissible for his daughter's son to marry among women."