So you want to have a simple way of sharing contact between several iPhones and iPads.
One way of doing this is to use a shared Gmail account.
In the past I was able to use the Exchange protocol on Gmail to sync between iOS devices, but for some unknown reason that doesn't work any more, or not reliably any way.
After lots of fiddling, I discovered that it is also possible to use the CardDav protocol to sync contacts
Manually configuring is trivial: Setting -> Mail, Contact, Calendars -> Add Account... -> Other -> Add CardDav Acccount.
Then configure it like this:
For easy deployment, I needed to create a configuration profile for this that has everything (except the password) pre-cooked
Using the iPhone Configuration Utility I could add all the settings, but it wanted to know one additional parameter: the "Principal URL".
This wasn't simpley "google.com", but it turend out to be this:
After this everything worked like a charm
The difference with the Exchange way of syncing is that CardDav doesn't use Push, but this wasn't really a problem for us.
An advantage of the CardDav way is that this only holds Contacts and cannot contain e-mail or calendar settings - hence no risk of accidentally using those.