A group of people having a conversation.
Multiple people talk to each other.
A multiple of things means a group of things; having a conversation requires that one or more people talk; and having a conversation generally means that at least two people are talking to each other except in rare instances of mental illness or loneliness so unless specifically noted otherwise conversations imply people are talking to each other.
Multiple people talk to each other is a rephrasing of a group of people having a conversation.
If there is a group there are multiple people.