Membership Plans can be closed at any time. Closing a plan prevents additional customers from purchasing it. Closing a plan does not deactivate it for anyone who has already purchased the plan but it will no longer auto-renew.
Coupon codes can be created specifically for members of a particular membership plan. If someone who is not a member tries using a coupon code that has this parameter, it will not work.
Although memberships do not have a sibling discount, a sibling discount can effectively be built into the plan by making it a family membership and setting the price and number of activity spots to account for multiple siblings. To help guide your customers, you can name it something like "Sibling Membership." Although this doesn't prevent a customer with only one child from signing up for this membership, the worst that could happen is that an only-child is signed up for the plan intended for a family and pays more than they would have otherwise!
A membership does not automatically enroll participants in scheduled activities. Instead, members can receive activity spots as a perk of their membership. These spots can be used by either the member or the provider to register for eligible activities.