What is the Sharia ruling on dealing with siblings who despise and hate each other? Is a phone call sufficient for maintaining kinship ties? And what is the ruling on not visiting a sister who requests that due to her brother's Sharia-compliant appearance?

You must reconcile your siblings and remove the hatred between them. It is not permissible for you to suspect your brother's wife of witchcraft unless you find evidence for it. Maintaining kinship ties is among the greatest acts of drawing closer to Allah, and severing them is a great sin. The lowest levels of maintaining ties are greetings and conversation, and the highest are visiting and giving money. The sufficient extent of maintaining ties is determined by custom.