How sync Mail across phone, iMac and Macbook pro

I have an iphone7, Macbook Pro and iMac. Macbook and iMac have Yosemite. I'm trying to get Mail to sync my Gmail account across devices (when I read an email on one device it doesn't show as "read" on another). I have read other posts and am still having trouble.

When I go on my Macbook and look up Mail>Accounts>Advanced I see that it says "IMAP prefix" and that box is empty. Port says 993 and the box for "use SSL" is checked. I interpret this as my account using an IMAP vs. POP.

On my phone I go to Accounts>Gmail>Advanced and for "Incoming settings" it says IMAP Path Prefix also, but there are no numbers next to this . Below it says Server Port 993.

I interpret this to mean that my phone is also set to IMAP vs. POP.

The Macbook is set to check for new messages "automatically."

On the phone under "accounts and passwords" the "Fetch New Data" is set to "push". In the "push" screen, My Gmail is also listed as Fetch every 15 minutes. To me this means that if I turn off push, data will be "fetched" every 15 minutes.

However, if I read an email on my Macbook, it does not show up as "read" on my phone or the iMac, so I'm having to delete or mark as read the same emails on every device! Driving me crazy. Any help is greatly appreciated.