(Y) Yes. Both parents of the siblings are the same.
Article 900 (4) of the Civil Code set out about this situation
(iv) if there are two or more children, lineal ascendants, or siblings, the share in the inheritance : inheritance of each shall be divided equally; provided that the share in inheritance of a sibling who shares only one parent with the decedent shall be one half of the share in inheritance of a sibling who shares both parents.
In this case, the siblings share the same parents with rge deceased (sometimes called whole blood siblings).
In other words, in this case, the legal inheritance is three-quarters for the spouse and one-quarter for all siblings. And one-fourth of them are siblings and will be divided by head.