Q: How do I share a group from my address book to another mac

You can also easily copy single contacts, multiple contacts, and single and multiple groups of contacts. To do so, select them in Address Book and drag them to the Desktop. The item(s) will turn into vCard files, which are generally compatible with all of today’s contact management applications. (I say “generally” because some applications don’t support vCards that contain multiple contacts.)

Above from:

http://www.macworld.com/article/1154974/addressbook.html

Also:

http://apple.stackexchange.com/questions/26632/how-can-you-email-an-address-book -group-to-another-mac-user