It is part of Islamic law that prohibits the marriage of close relatives. A very expansive answer is given on the link below
This is a debated topic. Some say a woman must have a mahram, others say it is not necessary if she will be safe.
Uncovering Face. Yes, Allaah has permitted elderly women to uncover their faces before non-mahram men, but that is subject to the condition that they do not uncover anything of their adornment that...