The current U.S. immigration law system for family members of U.S. residents and Citizens is a preference system. Unless your family member is considered an immediate relative of a U.S. Citizen their visa applications will be subject to annual quotas and the preference system.
The preference system gives priority to visa applications based on the nature of the relationship between the petitioner (U.S. Citizen or lawful permanent resident) and the beneficiary. For example, the 1st preference is for unmarried sons and daughters of U.S. Citizens.