I am originally from the Philippines and recently became a U.S. permanent resident. My parents and my brothers (who are unmarried and under age 21) would like to join me here. Can I petition for them to get green cards? Or, should I advise them to apply for visitor visas instead, and to return home to the Philippines afterward?
The immigration laws will not let you apply for a green card for your parents or brothers now. You need to become a U.S. citizen first. Depending on how you got your green card, your eligibility for U.S. citizenship is three to five years after you got your green card. (For more information, see Nolo's Becoming a U.S. Citizen: A Guide to the Law, Exam & Interview.)
After you become a citizen, your parents become your "immediate relatives," in immigration law lingo. When you file visa petitions for them and the petitions are approved, they'll be eligible to immigrate right away.
Your brothers won't be so lucky. When you become a citizen, you can file visa petitions for them, regardless of their age and whether or not they're married. But if the petitions are approved, they'll become "Fourth Preference" relatives and be put on a waiting list for a visa. The wait can be very long—in fact, brothers and sisters from the Philippines currently have the longest wait. The people getting their visas in early 2017 were waiting 23 years just to start the visa application process.
A tourist visa (B-2, visitor for pleasure), on the other hand, can be gotten in a few days. Being approved for one is not automatic—your family members will have to prove that they aren't trying to get into the U.S. permanently and that they can support themselves once they're here. (Once you become a citizen and file visa petitions for them, proving their intent to return will become harder, because they will already have indicated their interest in immigrating to the U.S. permanently.)
But once they've got the B-2 visa, it will probably be good for many trips to the United States. On each visit, they'll be allowed to stay for up to six months.
Just make sure they leave on time during every one of their visits—otherwise all manner of things could go wrong with their eventual hopes of immigrating. For more information on getting and using a tourist visa, see A B-2 Visa for Visiting the U.S. as a Tourist: Do You Qualify?