Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: Notification Based on Schedule
Yep! Simply have two notifiers (or pairs of notifiers), one for each person, and use Auto Pause schedules for the hours they shouldn't be used — i.e. so one is paused when the other is available, and vice versa. Then assign both to each relevant test.
You can use a similar technique to use different wordings or send different kinds of notifications (e.g. text message during the day, email during the night).