You want a process definition that will call one of three available subprocesses (SP1, SP2...

have SP1, SP2, and SP3 use the same input, output, and error schemas

define a template and use it to implement SP1, SP2, and SP3

use a Call Dynamic Process activity and select SP1, SP2, and SP3 as the alternatives

set an XPATH expression in the Call Process activity to determine at run-time the name of the subprocess to call

set one of the three subprocesses as the process name in the Call Process activity