I tried to reply to your post, but the code sections were blank, curious. Anyway, when you do this:
config setprop horde SharedAddressBooks enabled
You then need to do this:
signal-event email-update
Which adds this - 'use_shares' => true, - under the //40LocalSQL section. To now share an address book, you need to login to webmail, address book, you should notice a new icon - My Address Books. Create an address book, then assign permissions. If you really want to use groups, then you will need to create those groups via the horde admin section and add your users. It is pretty tedious to do at the moment, and may be getter if the distro moves to using LDAP for authentication as I believe horde can then be set up to query LDAP for all user and group info. But, that haven't been testing or confirmed by me.
John