Honestly it depends on what kind of communication is going on in your party. If it’s normal non-illegal stuff you would be fine using things like telegram and signal.

You will get privacy in a limited sense using a centralised application, even if it’s end to end encrypted because I don’t know how they handle the keys. The biggest issue with apps like signal and telegram is that they need your phone number. To avoid that you can use some Matrix instance maybe if that is an issue.