Add users to Blynk

Hello, @eyadalhasan yes you can invite new users in your organization
For example via Web platform:
Settings->users->create new users->invite via email

Also please read docs about limits Limits - Blynk Documentation

You users can download Blynk IoT app from Android(Google Play) and iOS(App Store) and login to this organization after registering via invite link in email.

Regarding settings for notifications, you can read the documentation and topics on the forum

About notification you can read Events, Notifications and the use of "Flag" variables