Originally only two person chats were e2e encrypted, then the added e2e to group chats, but last time I checked (admittedly a year or more back) if one participant in a group chat had an old version of the app, the entire group chat was unencrypted, without an obvious user interface indication of that.

I use (and trust) Signal. I believe Wickr is trusted by people who have resources behind them to know whether it's trustworthy (though it's closed source, so :shrug:).

If you need "used by the masses", then you're gonna be stuck with, I dunno - Facebook public posts? Gmail? Slack? Smoke signals? Nothing that's fit for purpose" if you value privacy...

Set up a webserver with teamspeak, which a ton of the millennial and zoomers already use for games, and nuke the server afterwards?