Is the paternal aunt sinful for visiting one of her male siblings and not the other, given the long distance?

The Sharia prohibits discord and estrangement among Muslims, especially among relatives, for severing ties of kinship is a grave sin. Both your paternal aunt and your father have a right to maintain kinship ties. If your aunt has ceased visiting your father out of estrangement, she is sinful. However, if it is due to a valid excuse, then there is no blame. Maintaining kinship ties is not limited to visits; it is also achieved through greetings, phone calls, and other means. It is not permissible for you to cut off your aunt and abandon your ties with her, even if she has cut off and estranged your father, because she is a relative with whom maintaining kinship ties is obligatory. The true maintainer of kinship ties is one who maintains them even if they are severed by others.