Some people are coming who the Losties originally thought would be good, but it turns out Ben might have been right when he said "every living person on this island will die." We know some Losties will escape, but most will not. And... that's about all we know from the trailers.

and what's the deal with jack's dad?

I've seen him in one of the trailers sitting in Jacob's chair, but I'm not sure what it means. There's a forum about it somewhere.