Reference: Fataawa wa Rasaa.il Mukhtaarah – Pages 557-558
Question: Is it permissible for a woman to uncover her hair, neck and arms in front of her mahrams – such as her father and her brother?
Response: Yes, it is permissible for a woman to have them – and that which is similar – uncovered in the presence of her mahrams.
And Allaah [alone] has the Complete knowledge [of all affairs].