This is an inappropriate situation. You should firmly and politely let your aunt know that such topics are not acceptable to be shared. For example, you can say 'Aunt, this kind of story is not suitable for us to talk about.'
Yes, it is clearly an inappropriate interest. Such a topic is private and should not be a subject of interest among people in this relationship. It violates the normal boundaries of friendship and marriage.
You might also need to have an open conversation with your wife. Explain the situation to her without causing unnecessary misunderstandings. Maybe she can help handle this delicate situation. For instance, she could talk to her friend and make it clear that such behavior is not proper in the context of your relationship.
This kind of content is not suitable for public discussion or sharing. It can make people feel uncomfortable and is not in line with the values of a civilized society. Instead, we should promote positive friendship stories that are based on mutual trust, support and respect.