Is it permissible for a man to hug his mother-in-law?

Answer

It is not permissible for a son-in-law to even shake hands with his mother-in-law. He may greet her and speak respectfully to her. He may not be alone with her nor is she allowed to travel with him even if his wife is present unless it happens to be an emergency. It is haraam for him to hug her. If he does so, and if he becomes sexually stirred even slightly when hugging her, then his Nikah with her daughter will immediately terminate, and there will be no way of them ever living as husband and wife. A new Nikah will not be valid between them.