Am I permitted to boycott my female cousins who verbally abused me, slandered my friend, falsely accused her of immorality, spoke ill of my relatives, insulted them, and did not backbite on my behalf, knowing that I will not boycott my uncle and will return their greetings if they greet me?

The kin with whom connection is obligatory are those relatives between whom there is a Mahram (definition) relationship. Connecting with paternal female cousins is not obligatory, and it is not permissible to abandon them for more than three nights, except in cases of religious or worldly harm. The abandonment ceases simply by greeting or returning a greeting. It is not permissible to accuse their mother of sorcery without clear proof. It is also not permissible to hit them for slandering your friend. Rather, you should gently forbid them from slander, backbiting, and other objectionable acts, and leave the gathering if they do not desist, as Al-Nawawi said: "Know that just as it is forbidden for the backbiter to utter it, it is forbidden for the listener to listen to it and approve of it."