Articles 214 and 216 of the Family Code speak clearly of situations when grandparents can exercise substitute parental authority over their grandchildren:
Art. 214. In case of death, absence or unsuitability of the parents, substitute parental authority shall be exercised by the surviving grandparent. In case several survive, the one designated by the court, taking into account the same consideration mentioned in the preceding article, shall exercise the authority.
Art. 216. In default of parents or a judicially appointed guardian, the following person shall exercise substitute parental authority over the child in the order indicated:
(1) The surviving grandparent, as provided in Art. 214;
(2) The oldest brother or sister, over twenty-one years of age, unless unfit or disqualified; and
(3) The child’s actual custodian, over twenty-one years of age, unless unfit or disqualified.
Whenever the appointment of a judicial guardian over the property of the child becomes necessary, the same order of preference shall be observed.