Hi Maurizio,
Thats correct, if you have a master suite that contains suites, the master suite will cascade down (flatten out) the execution for all the tests. So if the master is set to parallel, all tests in the sub suites will run in parallel. Here is a solution that may help you out.
In the example below
Suite 1 contains test a, b, and c
Suite 2 contains test d, e, and f
Suite 3 contains test g, h, and i
and you wanted to run test a,b and c in parallel, then run d,e,f in parallel while the suites are running serially, what you can do is make use of our invoke API (or LISA invoke). and create a driver test that has three REST step to invoke each suite via the invoke API rest service. I have included a link to the documentation on the Invoke API below.
LISA Invoke - DevTest Solutions - 8.0.1 - CA Technologies Documentation
Hope this helps. Unfortunately the reporting will be in separate reports, but this will give you an option if you need to stage your suites this way.
Thanks
-Joe