The most critical thing is that my sister has planed her son to stay here and not coming back to china. She wants her son to stay forever in the U.S, and I have not any control of her son because my niece will stay at his uncles.
I am willing to take care of him if he is here for a short visit---as the purpose of the B2 visa, but that is not his case. Besides, my niece is to young to come here.