(a) The petition for the termination of the parent-child relationship shall be filed with the court by:
(i) Either parent, when termination of the parent-child legal relationship is sought with respect to the other parent; or (ii) The guardian or the legal custodian of the child; or (iii) An authorized agency.
(b) The petition for the termination of the parent-child relationship may be filed with the court by a biological or adoptive grandparent acting in loco parentis to the child, where the child has resided with the grandparent for a period of not less than one (1) year and the placement is not under the direction of a juvenile court or the department of family services.