Jacob and Man in Black are the sons of Jack and Sawyer by Television Lady

When the LOST-ies are back in 1977, Sawyer and Juliet are shacking up. Amy asks Juliet when she and "Jim" are going to have one of these (babies) when Juliet helps her with baby Ethan. Juliet stammers and doesn't really give a firm committment but you'd think with her history as a fertility doc she would be on top of conception, as it were, preventing it OR facilitating it. Later when she, Sawyer, and Kate go back to the island from the sub to stop Jack from blowing off the nuke, Bernard regards her a bit cautiously and asks if she wants some tea. She has her hand over her abdomen kind of absently when he asks her this. And a gun in her jeans sticking out of the waistband.

Kate goes to Jack's place and completely jumps his bones the night before the Ajira flight leaves. The opportunity for conception is there. Why was she screwing him right then and there when she was very upset with him and all the surrounding circumstances?

This of course would mean that Juliet somehow survived the nuclear blast and was then well enough to gestate and give birth, and that the time travel would fling everyone back to the beginning of time, but it's not that far-fetched, considering all that's happened until now. Father/son pairs are crucial parts of the show. I'm thinking Jacob and the man in black are not going to be 2 randoms. . .