Is the division of titles in Spain ruled by any royal decree or civil law ? Which one ?

The late Duchess of Alba divided several of her titles among her many children.
Of course, the Alba title was kept for her eldest son.

The current Duke's son and heir has two daughters and the couple is expecting the arrival of their first son.
Is there any possibility the family will undertake a partition according to which the Alba title will pass to the 3rd child but 1st son ?