What should a sister do who wishes to wear the niqab but fears the hardship and difficulty of breathing, especially with her husband's brothers always present in the house?

A woman must cover her face from non-mahram men if she leaves her house or is in their presence. This is not exclusively achieved by the niqab, but by anything that fulfills the covering, such as lowering a garment. She must also adhere to Islamic guidelines when her husband's brothers are in the house to avoid fitna.