Linking the user to the group isn’t the hard bit (you can simply mirror the group and do it exactly the same way). When a user clicks follow, you’d do two actions - one to follow the event and one to follow the group.
It’s showing the group and the individual events in the same list which is troublesome. Is that what you actually want to to? If you were prepared to use two screens, you could make them look like tabs using this technique: Two list in one screen