Is it permissible to remove the Shar’i niqab in front of the sister’s husband who lives in the same house, provided there is no fear of temptation and no display of adornment, and in front of the paternal aunt’s husband who was a teacher in childhood within the home?

It is not permissible for a woman to remove her niqab in front of her sister's husband or her maternal aunt's husband, because they are not her mahram (definition). The Prophet, peace and blessings be upon him, warned against entering upon women, saying: "The hamwu is death." And because humans are weak in the face of desires, the Sharia (definition) has blocked all paths leading to the unlawful. Thus, it has forbidden tabarruj (displaying one's adornments), speaking softly (in a seductive manner), and wearing perfume when going out, because all of that invites fitna (temptation or discord). For Satan enters upon the righteous and others.