They are INSIDE their minds right now correct?
So you can't really hide "sadness" and "Pain" like if they were speaking
out in person. That's the main reason why you see such Expression out of Obitio,
That's what he is feeling. Those are the faces He was hiding the entire time he was mocking
Naruto. You don't have a real physical face in your brain, Just emotions.
Kishi drew them that way for a reason and it shows who Obito really is.