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> it only works if the the target process id is 0 and then it 
> generates the signal in all processes that share the console.
You can target a process group, which is a subset of the console's attached processes. That's why the console host, conhost.exe, routes dispatching the event through the session CSRSS.EXE, which handles bookkeeping of Windows processes and threads, including groups.
CSRSS creates a thread in each target, which starts at kernel32!CtrlRoutine. If a process is being debugged this routine raises a DBG_CONTROL_C or DBG_CONTROL_BREAK exception. Next it calls the registered handlers. The default handler, if called, exits the process with the exit code set to STATUS_CONTROL_C_EXIT (0xC000013A):
 0:000> u kernel32!DefaultHandler l3
 kernel32!DefaultHandler:
 00000000`76f31290 4883ec28 sub rsp,28h
 00000000`76f31294 b93a0100c0 mov ecx,0C000013Ah
 00000000`76f31299 ff15e1bb0500 call qword ptr
 [kernel32!
 _imp_RtlExitUserProcess 
 (00000000`76f8ce80)]
Example:
 import os
 import sys
 import signal
 import subprocess
 import threading
 STATUS_CONTROL_C_EXIT = 0xC000013A
 p = subprocess.Popen([sys.executable, '-i'],
 stdin=subprocess.PIPE,
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE,
 creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
 p.stderr.read(1) # poor man's WaitForInputIdle
 os.kill(p.pid, signal.CTRL_BREAK_EVENT)
 watchdog = threading.Timer(5, p.terminate)
 watchdog.start()
 exitcode = p.wait()
 watchdog.cancel()
 if exitcode < 0:
 exitcode += 2 ** 32
 assert exitcode == STATUS_CONTROL_C_EXIT