What we think we know...

You have to have Landry blood to be able to jump and you can only travel back in time, so far. So we know both KC Goodwin and Sam Bishop both carry Landry blood and they are from the future and jumping back in time which is landing them in our current day story. I think Elliott's mother jumped with Colton's older brother (which might be Sam, but why the name change) which is why he was not at Colton's wedding and they have not returned. This might be why Vic hates the Landry's so much. Also, Del's horse Lightning, like the Landry's dog must jump.

Am I close??