Um Firaas is a widow, she has a boy whose name is Firaas and a girl whose name is Farah; She married Maahir. The question: What is the relationship of the father of Maahir and his mother with regard to Faraas and Farah, are they like grandfather and grandmother because Maahir is the husband of their mother?

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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The father of Maahir and his mother are not Mahaarim (non-marriageable relatives) for Firaas or Farah, rather they are marriageable to them. For more benefit, please refer to Fatwa 84143.  

Allaah Knows best.