Using Pushover is very easy and has been extremely reliable for me and my family. You first get a Pushover Account via the Pushover site, and then buy Pushover for iOS from the Apple App Store. You can then load this on as many iOS devices as you'd like. When you sign into Pushover, using your Pushover credentials, a device will be created on the Pushover Servers for each of your iOS devices.
On the Hubitat side, Add a Virtual Device, and select the built-in Pushover driver. You will then need to enter your Pushover account's information in the device's user settings. The resulting Hubitat device can then be used in any App that supports sending Notifications. You can then add additional virtual Pushover Devices, if needed, for individual family members. Do NOT have them create separate Pushover accounts, as you don't want to have to pay the $5 for each of them. One account is all your need.
You can see more of the details here, but PLEASE do not use the driver code from this thread. Hubitat now natively supports the Pushover integration, so please use their driver. I am no longer maintaining my custom driver.
Official Hubitat Pushover Documentation is here...
https://docs.hubitat.com/index.php?title=Pushover
