Running the tests when instance is free

So here is my Question:
iI am working on a cloud project, where i have realm concept. Realms are nothing but an instance deployed on a service. So it means that 1 service say ABC have multiple realms like A, B, C, D…and so on. Now i have some 50 tests which i want to run on all these nodes parallelley. How can i achieve this?
I can create the TestSuites and TestCollections for the same, but what is need is, if a test is running on a realm A, and so on B and C, 4th test which has to run, should wait till the execution on the A,B and C are completed.

Did you get this? Let me know if more information is require.

Thanks in Advance.!!
Cheers!
Gaurav