Greencards--Accompanying relatives vs. preference relatives vs immediate relatives

Accompanying relatives are your spouses and children under the age of 21. They would get a greencard automatically when you get one so long as they can prove their relationship to you.
Brothers and sisters are not accompanying relatives.

Preference Relatives are a category of relatives on whose behalf a U.S. citizen or greencard holder can petition for a family based greencard. There are 4 basic preference groups. There are the 1st, 2nd, 3rd, and 4th preference. It is a hierachy of preference. The higher the preference the shorter the wait for a greencard. Preference relatives are usu. husbands, wives, children, (adoptive children maybe not) brothers, sisters. Cousins would not qualify as preference relatives. Neither would uncles. Neither would parents or grandparents.

Immediate Relatives are those relatives who can obtain a greencard through a U.S. citizne or greencard holder due to their familial relationship as an "immediate" family member. This group includes spouses (including widowers and widows if the death occurred within 2 years of the application) children under 21 with a U.S. Citizen parent, parents of U.S. citizens if citizen is over 21, step-parents and step children if marriage took place before the child's 18th birthday. Cousins, grandparents, uncles etc. would not qualify as an immediate relative.

***SPOUSES AND CHILDREN UNDER 21 YEARS OF AGE WOULD BE ACCOMPANYING, PREFERENCE AND IMMEDIATE RELATIVES.