Step 4:
Since your Author’s bylines are using “rel=author” and pointing to their Bio page you can go ahead and input a single link to your Google Plus Profile from your About Page using the “rel=me” micro-format as per the below example. You can place the link either as a Google Plus button or Google Plus Badge. You may go ahead and input the below in the header of the Author page:

<link rel="me" href="put Author’s Google Plus Profile URL here" />

Note: Replace the "put Author's Google Plus Profile URL here" with your actual one and leave the quotes.

You can learn on How to add Google+ Badge to your Wordpress Posts or Pages Here!