iCloud does not offer family accounts at the moment, and there is no migration path if you do have one. That may change in future, but I suspect Apple may not do it since iCloud is now free compared to MobileMe.
iCloud isn't big on sharing, so each family member will need their own account for email, calendars, contacts and device backups. Possibly consider creating a separate iCloud account that can invite the other family members to be events so you can "share" your calendars in that way, or just ensure that when creating an event on your account you invite the rest of the family.
You can however have one Apple Id to make purchases with. I do this since I have a American and South African account. My South African account is a fully migrated iCloud account for email, calendars etc.
My American account is simply an Apple Id and I use it solely for purchasing applications, books etc.
iCloud backs up all my devices to my South African account so I have backups of everything, and the purchase histories and updates goes through the American account. On my devices and in iTunes I am always signed into the App Store using my American account so never need to switch, iCloud on the devices is configured for my South African account.
For file sharing I suggest looking at something like DropBox.
