@Hilary232 " We are also going to cancel any reservations where the guest does not respond to our communications prior to check-in."
You can't just cancel reservations. You will get penalized for cancelling. A fine, your calendar blocked for the cancelled dates so they can't be rebooked, no chance of Superhost status and a "host cancelled this reservation" on your review page, which will discourage future guests from booking with you.
The whole point of requiring guests to submit requests instead of Instant Booking, is that you have the opportunity to vet them before accepting their booking. If there are red flags, decline.
And no, there is no way to flag others in the group.
So sorry you had this happen.