Is this the kind of scenario that you have problems with?

    parser = argparse.ArgumentParser()
    sp = parser.add_subparsers(dest='cmd')
    p1 = sp.add_parser('cmd1')
    p1.add_argument('-f')

    p2 = sp.add_parser('cmd2')
    p2.add_argument('-b')

    p3 = sp.add_parser('cmd3', parents=[p1,p2],add_help=False, conflict_handler='resolve')
    p3.add_argument('-c')

The problem is, apparently, that 'resolve' removes the '-h' option_string from the 1st subparser (but does not delete the whole action).  A kludgy fix is to add the '-h' back in (after p3 is created):

    p1._actions[0].option_strings=['-h']

'p1._actions' is the list of actions (arguments) for subparser p1.  Usually help is the first action (if isn't in p3 because of the parents resolve action).

I may work out a custom conflict handler function, but for now this appears to solve the issue.  I don't know if the patch I proposed solves your issue or not.