Question on S12 E23

And the writing shouldn't leave us this confused IMO.

I thought Dean made it pretty clear when he told Sam that despite Cas's faith in the Nephilim, Dean was putting his faith in himself, Sam, Mary, Cas and Crowley... sometimes. They were all in on the plan to trap Lucifer in the alternate reality. Cas introduced Sam and Dean to Alt!Bobby, who gave them an automatic rifle with angel killing bullets. Crowley entered the rift and put together the spell. It did seem like Mary was deliberately left out of the fight, but after half a season of angst over first Mary, then Sam lying about working with the British Men of Letters, I doubt that Dean would not have shared the detail of the plan with her.

Cas was the decoy- attack Lucifer and let Sam and Dean lure him to the rift. Once in the alt reality, Dean held off Lucifer while Crowley and Sam did the spell. It took a while for the spell to work; and it seemed like Cas's job was to stop Lucifer from coming back through the rift in the event that the Winchesters failed to hold him there long enough for him to be sealed in. However, after Cas spoke to Kelly, he seemed determined to take a more active part in protecting Jack- he stormed back into the rift and attacked Lucifer. Again, like the viewers, he must have known an angel blade wouldn't kill an archangel- but I think Cas thought stabbing Lucifer would slow him down enough for Cas to get out before the rift closed, sealing Lucifer in.

When that failed, Mary tried to knock Luci back into the alternate reality. I don't think she intended to get pulled in, but she had to know that attacking Lucifer with warded brass knuckles was going to put her close enough for him to kill her. She risked it to save her sons and to put Lucifer back in the alternate world before the rift disappeared.

Interesting thoughts, so you're saying that a cousin of Mary and a cousin of John would've had to have two kids, and Sam and Dean's story was passed onto them, but they failed?

Why do the demons look different there? That's something else I'm pondering.

See, I thought about one of Azazel's other psy kids leading the demon army, but then I thought about how Lucifer only sent him on that mission to find a special child, so that child would then kill Lilith. That doesn't necessarily change anything as any random psy kid could have presumably done that. And I guess the demons could've somehow found a random righteous man willing to sell his soul, so Alistair could break the first seal, and that random righteous man was the only one who could stop it, but didn't . . . maybe because he agreed to become Michael's vessel, and he wasn't strong enough as he wasn't a OTV . . . same goes for Nick, because I guess Lucifer still went to him . . . except that raises all kinds of questions about the prophecies in that universe that lead to Sam and Dean being and born.

Gabriel said the angels had always known it would come down to Sam and Dean, which is why the angels went about making sure the lines of Cain and Abel eventually lead to Sam and Dean. Does that mean that those prophecies weren't there or weren't the same, and if that's the case, then how much of it is because Sam and Dean weren't born, and how much of it is because the prophecies weren't there?

Yeah, I don't dispute that things after Sam and Dean being born were changed in those possible ways. It's the things that were changed prior to their birth that I'm questioning.