Is the wife entitled to ask her husband about the details of his relationship with his other wife, and is it forbidden for him to disclose those secrets?

It is not permissible for the wife to ask her husband for details about his relationship with his other wife, nor is it permissible for him to disclose her secrets, because that is considered the disclosure of a secret forbidden by Sharia. The husband must repent for what he has disclosed, and they both must refrain from discussing such matters. The wife should try to overcome her jealousy by showing affection to her husband and being a good wife to him. Jealousy between co-wives is natural, but one must treat her co-wife as she would like to be treated.