@BimboT50   you will have to write a custom logic for sending email on opening case (as per you need). pyEmailAddress property is an exposed property on Data-Admin-Operator-ID class. 

Few options you could use is - Flow action preprocessing activity or OpenDefaults activity on case class. But you will have to handle the scenarios like say 10 people opening the case not working on the case & 11th person works on the case. How many emails you expects your application to send out!

@BimboT50  you can browse the records in  Data-Admin-Operator-ID  and filter the records based upon your requirement.you can loop those records with comma reperated or semicolon seperated and you can set that value to param.cc or param.bcc based upon your business requirement and pass it to sendemailnotification ootb activity