We might need to hold off on Ikki and Jinora for the time being. In terms of Lin and Tenzin, it could just be them checking out their supposed hideout, poking where they shouldn't be. I don't see Xano and Xana turning them on purpose, unless the female (who I know was a fire bender but more reserved than her brother though I forget who was who, I think Xana was the girl) turns them back on purpose as a means to help them bring down her brother who could have given himself all elements?