I have created a shared calendar to update my travel/trek schedules (and sometimes those of my friends). For now, the calendar is lacking data entry big time 🙂 I’m sharing this more as a POC (proof of concept); something similar can be (and should be!) done for activity groups.
If there is such a need for your group, create one. If you need help, leave a comment or email me at blackfog at Gmail. For self-help, see Create and share a group calendar and Organize events with a group help articles.