Thanks for reaching out!
At the moment, we do not support alternating incident assignment per user on an escalation policy. When an incident is triggered, it will contact the on-call users in the order they are listed on the policy.
If you want Person 1 and Person 2 to alternate shifts, you can do so by creating a rotation on a Schedule. This wouldn’t guarantee that each user is assigned to every other incident, instead, it’s time based, so you can have them rotate every hour or day, etc.
It sounds like you may want to have Person 1 and Person 2 rotate being the primary and secondary on-call users. You can achieve this by creating two on-call schedules. So for example, you could have both schedules configured with the same rotation time and handoff time so that they are synced. Then your primary on-call schedule would start with Person 1 -> Person 2. Your secondary on-call schedule could start with Person 2 -> Person 1.
This way, each user would rotate responsibilities as the primary and secondary on-call users. On your escalation policy, you would assign your primary on-call schedule as the first rule and your secondary on-call schedule as the second rule. This would ensure that when Person 1 is the primary on-call, if not acknowledged, it will escalate to Person 2 and vice versa.
Also, to address your question about multi-user alerting, there will only be one on-call user per schedule. However, you can still notify multiple people at the same time by configuring this on the escalation policy - please see this article for more details on this.
I hope this helps answer your question, however feel free to reach out if you need further assistance!