My master A’lā Ḥaḍrat, Imām-e-Aĥl-e-Sunnat, scholar of Sharī’aĥ, guide of Ṭarīqaĥ, Ash-Shāĥ Imām Aḥmad Razā Khān عَـلَيْهِ رَحْمَةُ الـرَّحْمٰن explains the importance of observing veil with the brother-in-law, paternal and maternal cousins, husband of one’s father’s sister and that of mother’s sister: The following men – the brother-in-law, husband of father’s sister, that of mother’s sister, paternal and maternal cousins – are all classed as non-Maḥram for a woman. In fact, the harm of these men is more than the harm of totally unfamiliar men, because complete strangers will hesitate to enter a woman’s house but these (aforementioned) male relatives will not hesitate due to their informal relationship. A woman does not immediately behave in an informal way towards a complete stranger but she does towards these (aforementioned) men (i.e. she has no hesitation).
This is why when the Noblest Prophet صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم forbade men from visiting non-Maḥram women, one of his Anṣārī companions رَضِىَ اللهُ تَعَالٰی عَـنْهُ asked, ‘Yā Rasūlallāĥ صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم! What about the elder and the younger brothers-in-law?’ He صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم replied, ‘The elder and the younger brothers-in-law are death.’
(Fatāwā Razawiyyaĥ, vol. 22, pp. 217)
Question: How should a woman observe veil with her brother-in-law etc. when she is at her in-laws’ house? It is very difficult to stay veiled all day long? How will she veil her face whilst doing household chores?
Answer: Even at home, she must be careful to observe veil with her brothers-in-law. Ṣaḥīḥ Bukhārī states that Sayyidunā ‘Uqbaĥ Bin ‘Āmir رَضِىَ اللهُ تَعَالٰی عَـنْهُ narrated, ‘The Prophet of mankind, the Peace of our heart and mind, the most Generous and Kind صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم said,