Is the relationship between the questioner's wife and his brother's wife considered kinship ties (ṣilat al-raḥim), and are they sinful if they sever ties, and are the questioner and his brother sinful if they leave the two wives in this state?

Allah has commanded the joining of kinship ties and prohibited their severance. Scholars have differed on defining the "womb" (kinship) whose ties must be maintained. However, there is no kinship relation between the questioner's wife and his brother's wife that necessitates maintaining ties. Nevertheless, it is not permissible to abandon a Muslim for more than three nights; otherwise, the abandoner commits a sin, and the matter could lead to entering Hellfire. Thus, both wives incur sin through this estrangement, and both husbands incur sin for not forbidding this evil. They must hasten to reconcile their differences.