Apple made some new changes in macOS Mojave that require a small tweak before you can use Family Orbit on your Mac. After downloading and installing the app, before you run it you must follow these steps. In case you have already run it, you must restart your Mac after finishing these steps and relaunch Family Orbit from "Applications".
Click on the top-left Apple menu and choose System Preferences to open below Window. Click on Security & Privacy.
Now click on the tab "Privacy" and then scroll to the option "Full Disk Access". Tap on the ( + ) button.
Select "Family Orbit" from the list of Applications.
Finally, it will look like this, and now you can close this Window and launch Family Orbit.