Use an event’s sharing controls to invite another eligible group into the plan. The invitation must be accepted before the groups share the event. You can only use the groups and actions offered to your account.
The connected copies share the plan’s dates and changes. The organiser manages the shared plan; an owner in an invited group does not take over the organiser’s controls.
Cancelling the shared event marks all still-connected copies as cancelled. They stay in each group as history. Stopping sharing with one group unlinks that group and leaves an archive there; the event can continue in the other groups.
Together pays for groups. It does not itself connect events or share posts between them.