In deciding whether to speak up, you should consider two things. Firstly, how does their behavior affect you? If you can't readily answer this, then you're almost always better off staying out of it. The second is, what do you hope to achieve by speaking up? If you don't have a clear directive for mentioning it, then you run the risk of gossiping or tattling. Given that you weren't directly involved, I don't see many good answers to either of these questions so in your position I'd stay out of it. If Rhonda was bothered by their behavior, then it's up to her to say so, and if not, it's not up to you to intervene unless any or all of them report directly to you.