The unmarried child, if a part of the I-526 petition, will retain the green card. Once granted, the green card is not rescinded if the person later gets married.
If the I-526 petition has been filed then the principal applicant’s spouse may also obtain a visa.
However, Spouses of Children (dependent applicants) are not eligible to join the petition. As per EB-5 law, the green card may be given to only children below the age of 21 and unmarried at the time of application filing.