It's not up to you to determine your responsibilities, or anyone else's. It's not up to you to call out anyone else's lack of responsibilities. That is your manager's job. If your manager really wants you to “call it like we see it,” then you should call out your manager for his or her lack of responsibility. That's what should happen.
Your manager sounds awful, and scheduling time this week so you and your co-workers can gang up on the other co-worker is a terrible idea. Your manager is asking you and your your co-workers to conspire against another. That's not only unethical, it's possibly illegal. And why? To what end? Is that person suddenly supposed to realize they need to shape up? It's far more likely that the person will quit. It's even possible that the person may do something even more drastic if they are convinced they are hated by all.
This kind of thing makes sense in the military, where a unit tries to elevate a weak member to come up to a higher standard through peer pressure. But that works largely because the military is highly invested in bringing underperforming members up to standard, and because you can't just leave the military.
Do not conspire with your co-workers against another. Performance monitoring and performance improvement is your manager's job. At the meeting, simply state your responsibilities and nothing more. If you want to call out anything, then call out any responsibilities or tasks that are not covered when everyone else has spoken. Or call out that you feel overloaded with your responsibilities and are having a hard time meeting your commitments. But that's it. It's up to your manager to assign the uncovered tasks or balance coverage.