Did you do the casting?  I mean, did they WOW you at auditions and then become "lazy" later on down the line?  As for presence, not sure if it can be taught... but I think it can be enhanced.  I had a middle-schooler that I directed.  Loved her at auditions, but during production, she just was FLAT.  I spent a lot of time with her on character building... asking her specific questions to her character. For homework, I told her to go through the script and write me a short paragraph about her character's life.  The past, the present and where the character wanted to go.  She really got into it, and ended up creating an excellent backstory for her character.  She was GREAT in the end!!!