ChainsawAsh said:
The last thing I'll say about Force ghosts - you don't have to have Luke look at them at all, just them watching Luke as he says goodbye to his father would be poignant enough.
Luke somberly burning the body of his father, and Yoda, Obi, and his father's GHOST look on with goofy grins on their face. Might feel a little incongruous.