If the principal beneficiary becomes a green card holder, the immediate family, ie spouse and minor children can file following to join if they have not filed together. The requirements are enumerated in 9 FAM 40.1 N7.1 General
There is no time limit to file this petition, provided that the Legal Permanent Resident (LPR) has not left the country. Minor children, if they are in US can adjust, no accrual of illegal stay (under 21) However the relationship should still exist, ie the child has not reached 21 years of age, got married, or the LPR has not died. The relative should consult the consulate, fill out a DS-230. Documents should include all of the LPR’s Immigrant visa petition, and a copy of the Green Card (Permanent Resident Card) and documents to establish the relationship, like marriage certificate or birth certificate. The LPR has to also file the I-864.

For more information contact Houston Immigration Lawyer or Houston Immigration Attorney, Annie Banerjee