Is the grandfather’s wife a Mahram woman to the grandsons?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Allaah The Exalted Says (what means): {And do not marry those [women] whom your fathers married, except what has already occurred.} [Quran 4:22]
This verse indicates that it is impermissible for sons to marry their step-mothers, whether or not the father consummated the marriage. Actually, this ruling applies to the grandfather’s wife, the paternal grandfather and the maternal grandfather, parent and grand parent up to all levels. Moreover, this ruling is applied to the wives of fathers of all levels, whether they are entitled to inherit from the son or not and whether fathers are from blood or nursing relation. This ruling applies to the wife of one’s father or grandfather’s wife, paternal grandfather and maternal grandfather, and fathers of all levels. Muslim scholars were unanimous in this regard, as Ibn Qudaamah clarified in his book Al-Mughni.
Allaah Knows best.
You can search for fatwa through many choices