"Follow to Join" is a term of art. Your spouse and children are eligible for "derivative status" - visas given to spouse and children who accompany the principal beneficiary, or enter the U.S. If the entry is within 4 months of the principal beneficiary's entry or appearance at a consulate abroad, then they are supposed [...]

Permanent residents are required to maintain a permanent residence in the U.S. Any absence abroad that extends beyond six months raises the presumption that the Green Card holder has abandoned his or her permanent residence in the U.S. The Green Card holder then has the burden of overcoming this presumption when they attempt to re [...]

There is an entire process involved and would require you to file an Immigrant Petition (I-130) and process an Immigrant Visa Application with the National Visa Center. The USCIS website has an excellent overview of the process. See: http://www.uscis.gov/family/family-us-citizens/spouse/bringing-spouses-live-united-states-permanent-residents. Alternatively, you could engage a Law Firm to take care of the paperwork. [...]