Lizzie and Leonardo have adjusted just fine to being "brother and sister." They love to plan and run back and forth. Lizzie barks and pretends to snap at Leonardo (or Leo as I usually call him.) And Leo leaps over Lizzie, and bats Lizzie around, with his claws safely sheathed.
But for all their chasing and playing, I was very happy to catch this sight the other day. Leo and Lizzie catching a few zz's together on the couch after an active morning.