Purdah

Observing purdah from one's daughter in law's father

Q: My dad is late (may the Almighty grant him jannat). He has left behind 2 sons and 2 daughters. The eldest son lives with his father in law.

After mummy's iddat, it was her desire to perform umrah and her second son took her Alhamdulillah. The elder son wants to take my mother, his wife and his father in law, who is also a widower, for umrah. Will it be permissable for my mother to travel like this in the company of his father in law?

Are the children of one's adopted father's second wife mahrams?

Q: I'm adopted by my parents. My adopted mother then breastfed me so they became my foster parents. In 2021, my mother (foster mother) passed away and my father got married to another woman. She already has three children. Are they mahraam to me? Should I have to make purdah from them? Is it permissible to marry them at the same time?