The definitions you are using are not the same as mine, that's why I've suggested taking a look at the Wikipedia entries.
Every process has at least one thread by definition, and a thread owns its copy of the register set (so must run on one core).
In Unix, the Shell (command line interface), for example, forks. I have suggested that the API could be split off from the OS, and this could fork. Of the 20+ contexts that you counted, how many could be naturally replicated by a fork?
Compiling a switch statement to a jump table is an optimisation. Copy on Write is one way in which forks are implemented. The child process shares the same physical memory as the parent until either parent or child writes to it, at which point it is copied.