PS4 Confused about who needs a PSN account
Solution 1:
Unfortunately, in order to use the PlayStation Network each account needs to use a unique email address. What you've done is correct for your setup. For PlayStation Plus, you should only purchase it for the main (master) account you set-up.
If you set up the console as your Primary device, the subscription can then be shared with the other accounts on the system, without the need to purchase separate subscriptions. This video shows how your account can be set as primary: