Is it sufficient to inquire by phone about relatives who sow discord between the questioner and his father, in order to avoid the problems that result from visiting them?

The matter of kinship is great in Islam, and severing ties of kinship is among the major sins. A person who severs ties of kinship will not enter Paradise. You must maintain ties with your relatives even if they treat you badly, in accordance with the Almighty’s saying: "Repel evil with that which is better, and then the one between whom and you was enmity will become as though he were a devoted friend." Furthermore, patiently enduring their harm will not affect you, as the Almighty says: "But if you are patient and fear Allah, their plot will not harm you at all."

If you fear problems from them, fulfill your duty of maintaining kinship ties by calling them and asking about them, for abandonment is not considered maintaining kinship ties.