Unfortunately there is not a visa category for niece, nephew, aunt, uncle or cousins of United States citizens or legal permanent residents (LPR). A petitioner (U.S. citizens or LPR) may sponsor four categories of relatives. Parents, spouse, children, brothers and sisters. In some situations, with a lot of patience, you may be able to eventually bring over your extended family members by first sponsoring a relative that is included in one of the four categories listed above. For instance, you may petition for your brother and once his visa number becomes available he may bring his wife and children as derivatives. Hence, your nephew and niece (if under the age of 21) are allowed to come with their father, your brother. Another example is that you could sponsor your parents. Once your parents naturalize, they may sponsor their brothers and sisters. In the end you were able to bring to the United States your aunts, uncles and cousins as derivatives.