Wife’s family making the husband have doubts about his wife

One of my friends came to me to ask my opinion about a problem that he is facing. He says that there was a big argument between him and his wife’s family, so his wife’s family started making him have doubts about his wife and telling him that she had been betraying him from the first day of marriage until now (approximately fifteen years). All of this was done by hints, not stated bluntly, but these were obvious hints that were made repeatedly. They got other people to help them in that so that he would divorce her, and now he is suffering from waswaas (whispers from the Shyatan). It should be noted that they have children and that the wife prays regularly, always on time. This has led to strong rumours circulating among people and the husband is living in isolation; no one visits him, not even his brothers, because of these rumours. When he confronted his wife she denied it vehemently and did not speak to him for several days, even though when the disputes between him and her family grow intense, she behaves in a manner that causes him to have doubts about her and there are times when the husband believes these rumours and times when he thinks that they are untrue. He often thinks of divorce because she has caused him problems in his social life and at work and with his brothers. It should be noted that the husband has never seen or heard his wife speak to any stranger (non-mahram man). What is your opinion? May Allaah help you to do that which is good for this ummah.