From the little I've read on twitter, Jose Molina, Elijah know Kol's death, but chose to move on, without rancor.
J.M. says that Elijah is different from Klaus and Rebekah, his way of reacting is another.
Elijah got upset with Katherine, for a matter of confidence. After all were partners.
I don't understand that either ^ The writers severely f*cked up Elijah's character in this one episode. 'Do anything for his family'... hmm, really?
Someone else in a LONG list that just decides to disregard everything Elena does, just because it's Elena. And this 'compassion' crap? How is she compassionate when she willingly went along & organised 2 plans to kill thousands of vampires?!- And not feel the slightest bit guilty about it.
I really should be over this by now.. but I'm not.