What is the Family plan?
The Family plan is Premium for up to 4 people, including you. You pay once, and everyone you invite gets full Premium on their own account.
Everyone keeps their own account
This is the part worth being clear about: the Family plan pays for Premium, it does not put anyone into a shared calendar. Each person signs in with their own email and keeps their own calendars, their own tasks and their own settings. Nobody on the plan sees what the others are planning — not the other members, and not you as the owner.
If you do want a calendar you plan together — a shopping list, a family schedule — that is a separate feature, and it works on any plan: just share a calendar with whoever you like. The two are independent. You can share a calendar with someone who is not in your family, and putting someone in your family does not share anything by itself.
What it costs
$9.99 per month, or $89.99 per year. Compared with four separate Premium subscriptions, the yearly plan is the one most families pick.
What each person gets
Everything in Premium: unlimited calendars, calendar sync (Google, Outlook, Apple Calendar and Apple Reminders), reminders, recurring tasks, subtasks and checklists, file attachments, extra colors and themes, and export.
How the seats work
You hold one seat as the owner, and you have three more to hand out. A seat is not a payment — the person in it is never charged, and there is no subscription of theirs to cancel. You can remove someone and give their seat to somebody else at any time.
If you cancel the Family plan, everyone keeps Premium until the end of the period you have already paid for, and then all four accounts move to the free plan. Nobody loses any data.