To share your PS Plus benefits with other users on the console, you have to activate your console as the primary PS4 for your PS Plus account. It's not enough to just have a Plus account on the console.
Have a look at the PS4 User's Guide for more information about activating a PS4. Here is an excerpt:
You can activate only one PS4™ system per account.
When you activate a system, other users of the system can use applications and enjoy some of the PlayStation®Plus benefits of your account, even if that user is not logged in.
Activating your system
The first time you sign in to PlayStation™Network, you normally choose to activate your system. To activate your system after you first sign in, select (Settings) > [PlayStation™Network/Account Management] > [Activate as Your Primary PS4] > [Activate].
Deactivating your system
Select (Settings) > [PlayStation™Network/Account Management] > [Activate as Your Primary PS4] > [Deactivate] on an activated PS4™ system.
You can deactivate a PS4™ system only from that system. Deactivate your PS4™ system before transferring or disposing of it.
If multiple users have activated the system as their primary PS4™ system, deactivate it for each user.