KittyMommy,be patient I am sure one of our kitty-gurus will come along soon.
From my own experience,cats do mourn the loss of a sibling or a buddy and I would think especially since Freddie grew up with George.
As for introducing a new kitten to him,we have a Sticky somewhere on the Forum,about just that,I am not sure where to tell you to look though.
So sorry you lost little George
little one.