Our two both sit and sit/stay very well but have a slight problem with the down.
Milly will go down but after a few seconds boredom seems to set in and she'll stretch her back legs out while lowering her head between her front paws, eyes looking up with a definite "treat required" expression

Chaz does the opposite, he goes down and then rolls onto his back, rear legs stretched out and starts pawing the air with his front paws. I think I'm the cause of this as he really didn't like his paws being handled as a puppy so I used to play with his front paws to get him used to them being handled

(Usually to the tune Patty-cake, patty-cake, baker's man……)

Bob.