Membership permissions - BP groups

Hi folks, need a bit of advice

We run a wp multisite and buddypress install at

The way I use membership premium at the moment is really as a "gatekeeper".

Visitors i set in membership to only have access to certain pages and NO buddypress access

People that sign up for free (become subscribers) have access to BP pages.

We don't want "strangers" or visitors to see a users BP profile or visit the activity wall.

Issue, i am not clear on how to set is that if a BP Group has been set up as public, I would like visitors to see the group home page ...

If a group is private well then obviously not. What is the easiest way to apply this rule in membership?