N.Y. Dom. Rel. Law § 71
Where circumstances show that conditions exist which equity would see fit to intervene, a brother or sister or, if he or she be a minor, a proper person on his or her behalf of a child, whether by half or whole blood, may apply to the supreme court by commencing a special proceeding or for a writ of habeas corpus to have such child brought before such court, or may apply to the family court pursuant to subdivision (b) of section six hundred fifty-one of the family court act; and on the return thereof, the court, by order, after due notice to the parent or any other person or party having the care, custody, and control of such child, to be given in such manner as the court shall prescribe, may make such directions as the best interest of the child may require, for visitation rights for such brother or sister in respect to such child.
N.Y. Dom. Rel. Law § 71