Something we call the Force...

In ROTJ Luke says he cannot kill his own father(Vader) then Obi Wan says the Emperor has already won.

No, in ESB Gordon, not ROTJ.

I think it was because Luke was being unruly and was doing the whole "I have to go" thing. He hadn't finished his training and Obi-Wan was thinking that Luke was either going to a) get diced into bantha bites or b) fall to the Dark-Side.

That is not the quote I was thinking of.

Yeah, Gordon's right, Rexy, yerssot was asking about an ROTJ quote.

Obi-Wan thought Vader would have to be killed because he had already failed to do what Luke ended up doing.

"Obi-Wan once thought as you did," says Vader, when Luke talks of the good he can still sense inside Vader.

Oh, sorry. I haven't seen ROTJ in awhile.

which type of force do you guys think the Emporer and Vader use?

Errr... it doesn't really work like that. Everyone just uses 'The Force', just the Force is a wide-ranging concept and some prefer some aspects of it to others.