Now you see that I was not joking. But I think it is useful to clarify the definition. The definition of a “possible world” is a “state of affairs, which is different from our existing world is some aspect”. That is IT. There is nothing else. If you have a problem with it, there is no reason to continue. But I hope not. It is a very simple concept.
I don’t, because it is irrelevant. We are NOT concerned with cosmology or cosmogony. The thought experiment starts with our existing world - which is physically possible, since it exists. We can postulate a different world, for example, where there is an oak tree, instead of a pine tree at a certain place. Or another world where Hitler was a stillborn, and as such there would be no Holocaust. How could that happen, is none of my concern. It is just another “possible” world. Not just logically, but physically possible. And whatever is physically possible, it is also metaphysically possible - adding again - whatever that might be.
Causal antecedents are only applicable for events within a world, but inapplicable for the “world” itself. That would assume that the world “needs” an outside creator, and that is what you might wish to establish. It is a logical fallacy to include your “wished for” result into the argument itself, it is called “begging the question”.
The proof I presented starts with the existing world. We apply certain transformations, being mindful that the transformations should not “introduce” a logical impossibility. Eliminating parts of the existing world cannot introduce logical contradictions. Removing all the galaxies, except the Milky Way would make a “simpler world”, but still possible. Then eliminating all the solar systems, except ours, would make the world even simpler. This kind of gradual elimination process always yields in another, simpler “state of affairs”. Finally, when we are at a very simple world, we eliminate everything except an “up” quark - in one case, and eliminate everything except a “down” quark in the other case, hereby creating two possible worlds, without any overlap. And that takes care of the “necessary being”.
This process does not care about “God”. It simply gets rid of the concept of necessary being. You are welcome to worship the God of the Bible. I read some time ago: “Everyone believed in God, until some philosophers tried to prove his existence”. You cannot. Be happy with your faith, and leave reason alone. As Luther was fond of saying: “Reason must be trampled underfoot” and “Reason must be made the handmaiden of faith” - and he said that when he was a well-respected Catholic theologian.