Hi Sahana,
I would like to think and hope that in your example only one license would be required when running a process that calls several sub-processes. (process A calling both process S1 and S2, depending on the data)
With the best practice rules prescribing to define sub-processes for re-usable chunks of logic in either objects or sub-processes, it would be greatly counterproductive of BP to require multiple licenses to run such a beautiful construction.
------------------------------
Happy coding!
Paul
Sweden
------------------------------
Happy coding!
Paul, Sweden
(By all means, do not mark this as the best answer!)