It is a problem indeed. We found the best solution to #2 is to avoid any massively niche topics. For example, "has anyone used <specific Python library>" isn't

It is a problem indeed. We found the best solution to #2 is to avoid any massively niche topics. For example, "has anyone used <specific Python library>" isn't great for a group conversation: it instantly excludes people who haven't used that library, as well as people who don't know Python. Instead we try to stick to topics which everyone can relate to (even weakly), e.g. process-related topics are great for this.