Hi soro,
This scenario involves three entities—case, queue and queue item.
Case and queue item is 1:N relationship(Object lookup field), queue and queue item is 1:N relationship(Queue lookup field).

When a case has added to one queue, one queue item will be created automatically.

You can set workflow as following steps:
1.Go Settings > Process to create a workflow in queue item entity.

2.Set trigger.
when one queue item change to another queue, queue lookup field value will change.

3.Add steps.
(1)Check Condition
Specify the queue item from case and it has added to two privacy queue(test1 or test2).

(2)Send email.

(3)Default action--stop workflow.
if the queue item is not from case and it hasn't added to the privacy queue, you can stop the workflow.

Regards,
Leah Ju
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