Yes, it is appropriate to make fun of celebrities as long as their families are not brought into the spotlight. We should be able to critique people in show business based on their actions and statements. Their families, however, should be left alone. There is no reason to bring them into it.
It is completely appropriate to make fun of celebrities. They put themselves in the public eye, knowing full well that they will be scrutinized. This goes with the territory. Besides, we all like to laugh and it says a lot about the celebrity if they are capable of laughing at themselves.
When a person becomes a celebrity, they are in the public eye. It's fair game to make fun of them. Most of the time, celebrities are well paid for what they do. In exchange, the celebrity has to know that they are fair game for the occasional mean tweet, or for something silly they say.
Being made fun of, judged and ridiculed are part of the job of being a celebrity. If you're constantly in the public eye you will be judged and ridiculed so celebrities should not be sensitive to this. This is part of the reason why many celebrities can't handle the spotlight.