Are the grandfather's wife and her daughters considered unmarriageable relatives (mahram), based on the prohibition of marrying the father's wife, even if through a higher degree of ascent?

The wife of the grandfather is forbidden by affinity, due to the generality of Allah's saying: "And do not marry those [women] whom your fathers married," and the grandfather is considered a father, as stated in the story of Yusuf and Ya'qub's brothers. As for the daughters of the grandfather's wife, they are not considered mahram to you unless they are the grandfather's own daughters.