It's possible to killl some of the jedi masters and still stay on the light side!
if you are completely or half way into the light side and your on nar shaddarr for example and your talking to Zez kai-ell he offers to fight you, down side is you might get a few dark side points but you'll get them back again
i'm not sure about vrook and kavar but zez kai-ell can be killed.