After months of testing, Google has announced that all group chats that have RCS enabled in its Android and Wear OS Messages app now have end-to-end encryption (E2EE) enabled by default. That should help keep prying eyes away from your chats as only the group participants will be able to read your messages, as long as they're not sharing screenshots or showing their phone to someone next to them (there's not much you can do about that, unfortunately).
Google notes that RCS will now be enabled by default for new and existing users, as long as they haven't previously switched off RCS in their settings. So, maybe make sure that no one in your group has opted out of RCS before you start sharing your most private information.