Show notifications for all users
I'm sorry there is  no way you can receive the notification of the other user, because according to the concept of 'Users' in android each user represent a different physical user of the device. So the privacy won't let you receive notification from the other users.

Instead of going for another user, you can try 'Managed Profile' which create a separate profile but which belongs to the same user. In the underline architecture you will get almost all the security protection of a separate 'user' to this profile. The main difference will be they are in the same launcher.

Thanks.