When you delete the iCloud account, you're asked if you want to keep everything on your iPad. If you agree, you won't lose anything.
The iCloud account is nothing else than an Apple ID, so it would be best to choose one of the existing Apple IDs as iCloud account for all of them, if you just want to try it.
When you look at Settings - iCloud, you'll see what's synced between iDevices if everything is enabled. If you use Keychain, passwords and autologin information will be available everywhere else as well.
Settings - iCloud is also the place to remove the account and sign in again.