There are few questions, any entity can go to anywhere or Entity1 go only to a concrete server and the other goes to the other.
Do you want if the worker is processing the entity with the lowest priority and the bigger priority comes to the server, the worker stop their tasks and goes to the bigger priority to star with the task?
There are a simbit called, interruptibleoperator, maybe it can help you.
I'm interested in this, because I have the same problem, but i have only one kind of entity and I want that the operator move between three servers.
Server1 -- Server2 -- Server3
An entity comes to Server1 start the job, finish and the entity goes to Server2 and another arrives to server1 and the operator start with the tasks, but before finish, the entity in the server 2 pass to the Server3 and the operator need to pause anythin that they are doing in the server1 and goes to the server3 to make some task, when he finish he has to come back to the server1 to finish the job.