Many of my Bronx clients want to know how to get a green card for different family members. Non-immediate family members like cousins, grandparents, aunts and uncles etc. are all parts of our extended family that we want to help. Although you will not be able to directly petition for them, you can let them know how they can legally come to the US to live.
The only people that can petition for them are immediate relatives, such as a US citizen parent, child 21 or older, sibling or spouse. Spouses or parents who are permanent residents can also petition for them. You can help them if their relative does not have enough income and you would like to be a "sponsor" for them.
If there are no relatives to help petition for them, they could try to get an employment based visa. Whether or not they can get this type of visa would depend on their education and skills as well as the type of profession that they are in.
If they cannot meet the requirements for an employment based visa and are thinking about going to a university/college, then they can try to come to school in the US and get a student visa. This does not mean they will have permanent residence in the US, but they will be able to attend school and perhaps obtain employment which could lead to getting a green card.