I had a Family Plan in MobileMe, does the upgrade apply to all my family's accounts?

All iCloud accounts are free and each includes 5 GBs of storage.

When you migrated your Family Pack accounts - each sub-account needed to be migrated separately, so I hope you did that - each became an individual iCloud account quite separate from the others. The Master Account was given the complimentary additional storage, now extended to 30 September 2013, to compensate for losing the iDisk; but the sub-accounts (which you will remember had only 5GB each of iDisk) got only the standard iCloud accounts with 5GB free storage.