Is it permissible, in Islamic law, to continue shunning the husband's family after repeated problems and accusations that have reached the point of slander?

The cohabitation of the husband's family with the wife in one house may cause problems, and the wife has the right to an independent dwelling. It is not permissible for Muslims to boycott one another except for a legitimate purpose. So, if your boycotting of your husband's family is to avoid their evil and harm, then there is no blame. If your husband's mother accuses you and causes discord between you two, then she is doing wrong and acting unlawfully, and she should be advised with kindness. Displaying a knife is also forbidden. We advise patience and striving to reconcile differences.