Thanks.
So if 2 people are playing on the same account and there are no sub accounts, what would both be called? SonnyBoy is online as SonnyBoy as he is the 'BUYING' Account and PS+ is registered to him. What would BigDaddy be online as? Surely it can't be SonnyBoy? I think I get it as you're saying that it knows I am another account on the 'Buying' machine/another user on SonnyBoy's machine and therefore it would just automatically allow me online as another user, therefore, as BigDaddy and no actual sub-account.
Also are you saying that I could only be online (BigDaddy) and play Killzone IF my son (SonnyBoy) is playing that game online at the same time?
If you mean on different consoles, it's not happening. You'll need to create another account on the main user's home console. That user receives all the benefits afforded to the main user as long as they're on that user's home console.