Is mentioning news about people, such as their travels, illnesses, or one of them marrying a wife in addition to his current one, considered backbiting them?

Backbiting is mentioning about your brother what he dislikes of his faults that are present in him. If they are not in him, then it is slander. As for talking about people's affairs, such as their travels, illnesses, marriages, and so on, if there is nothing in it that offends the person being talked about, then it is not backbiting and is permissible. However, one should not talk excessively about matters that have no benefit; as the Prophet, peace and blessings be upon him, said: "Whoever believes in Allah and the Last Day, let him speak good or remain silent."