I think everyone has jumped on this train and is watching.
Brock, I doubt he would know about that unless he is working with others. It did not appear so. More of a motive for Jesse.
Walt's family, he may watch from a distance. Maybe visit Holly at school or something.
Grey Matter, it would not surprise me if he left evidence that tied them to the meth operation.
Jesse, I think may end up saving Walt despite their differences.
Lydia, would probably off herself if backed into a corner or something equally stupid.
Uncle Jack and the gang, I'd expect this is what the ricin is for. The gun is just back up. Not sure how. Either that or it is for Walt himself if he is caught.
Todd, may live for a while. Someone needs to give up the location of Walt's money.