I just use one account. This way we have a shared calendar for all and shared contacts. It makes it nice as our phones are basically identical so contacts and calendaring on her phone is on mine as well. This way we know who is doing what at any given time. Of course we each have our own email accounts, contacts, and calendars for work and personal emails accounts. We sync to iTunes so are not worried about iCloud back ups.
This used to be ok but it's not anymore. (I recently switched away from a setup like what you describe.)
For starters Siri will think you're all the same person. It syncs the "Call me x" information across all devices. So Siri requests like "
E-Mail mom" or "
Text my son" won't work for most of the family.
In addition, more and more apps and games are storing their data and saved states into iCloud so you'll start running into more and more problems with apps as time goes on. (Public Photostreams is a good example of a place where your "everyone shares" plan no longer works very well. Watch as you all comment on a photo and have it all appear to come from the same person.)
The best method these days is this:
1) Main iCloud account: Everyone gets their own iCloud account. Turn off contacts and calendars in here.
2) If you don't use iCloud email, set up your personal e-mail second.
3) The FAMILY iCloud (Don't use dad's...make up a whole new iCloud account JUST for this.) Set this up after you set up the main iCloud account but use this one for contacts and calendars.
4) App Store: Log in to everyones phone using dad's account
5) Facetime and Messenging: They already should, but make sure they match everyone's own main iCloud settings.
I just cringe at the thought of having to see everyone else's appointments next to mine on the same calendar haha. Too much clutter and I would just personally prefer to only share what is needed to be shared, but that's just me.
Even within a single account you can make different calendars. I have a [me], [wife], family, and work calendar all within a single account. You can turn any of them off but still have the ability to turn them on when you need them.