Welcome to GSD puppies!! They are stinkers!!! What your pup is doing us very common. I would have your girls get more involved in his house manners training. Have them feed him, do basic commands and the like. Teach your girls how to handle him.
It takes some pups many many months to stop this, unfortunately they keep growing, so best to get your girls involved in his training. He will learn to look to them for direction and they can learn the appropriate way to redirect and correct if needed.
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