When is a Muslim considered to be severing ties of kinship, who are the kin included in that, is a person considered to be severing ties of kinship if their communication with their sisters decreases after a dispute, and is maintaining ties of kinship obligatory only upon men?

All those to whom you are related by lineage are your kin (dhawu al-arham), and it is a religious obligation to maintain ties with them. The Sunnah (definition) has encouraged learning about genealogies in order to maintain ties of kinship. Kin are of two types: maharim (unmarriageable kin), with whom it is obligatory to maintain ties and forbidden to sever them; and ghayr maharim (marriageable kin), with whom it is recommended to maintain ties and disliked to sever them. The obligatory maintenance of ties and the forbidden severing of ties are determined by custom ('urf). Therefore, whatever custom deems to fulfill the maintenance of ties and negate severing is considered to fulfill the obligatory maintenance of ties. The misconduct of a kinsman does not negate the obligation to maintain ties with them, unless it causes harm to the one maintaining ties. The rulings regarding maintaining ties of kinship and their obligation apply equally to men and women.