Buddypress – adding custom post to members

There are more problems:

1) Add the activity on adding meeting

You could use the save_post hook to add activity, but I’d rather add custom notification, as the activity item can be easily missed. The how to is described in this great tutorial https://webdevstudios.com/2015/10/06/buddypress-adding-custom-notifications/

2) Let the users view the post

You should save post_meta with the array of user ID’s, and than just compare with if (in_array(get_current_user_id(), $invited_users_ids)).

3) Let user edit the post

Depends if on frontend or in the admin? If on frontend, just create a custom template, check if the user is allowed to edit the post, and build a form for editing the post. If in admin, there are multiple ways to do this – using add_cap would be one, using pre_get_posts filter another