See:
G.R. No. 194066, June 04, 2014, REPUBLIC OF THE PHILIPPINES, PETITIONER, VS. FRANKLIN M. MILLADO, RESPONDENT.

"x x x.
The registered owners appearing in the title sought to be reconstituted, or in this case, their surviving heirs, are certainly interested parties who should be notified of reconstitution proceeding under Section 12 in relation to Section 13 of R.A. 26. Indeed, for petitions based on sources enumerated in Sections 2(c), 2(d), 2(e), 2(f), 3(c), 3(d), 3(e) and 3(f), Section 13 adds another requirement aside from publication and posting of notice of hearing: that the notice be mailed to occupants, owners of adjoining lots, and all other persons who may have an interest in the property.[ Notwithstanding the sale supposedly effected by vendors claiming to be heirs of the registered owners, they remain as interested parties entitled to notice of judicial reconstitution proceedings.
It is settled that the actual notice requirement in Section 13 in relation to Section 12 of R.A. 26 is mandatory and jurisdictional.[4] In the early case of Manila Railroad Company v. Hon. Moya, et al.,[5] this Court categorically declared:
It is clear from section 13 of Republic Act No. 26 that notice by publication is not sufficient under the circumstances. Notice must be actually sent or delivered to parties affected by the petition for reconstitution. The order of reconstitution, therefore, having been issued without compliance with the said requirement, has never become final as it was null and void. The Manila Railroad cannot then complain that the motion to set aside was filed beyond the reglementary period. (Emphasis and underscoring supplied.)
Where the authority to proceed is conferred by a statute and the manner of obtaining jurisdiction is mandatory, the same must be strictly complied with, or the proceedings will be void. As such, the court upon which the petition for reconstitution of title is filed is duty-bound to examine thoroughly the petition for reconstitution of title and review the record and the legal provisions laying down the germane jurisdictional requirements.[6] Thus, we have held that notwithstanding compliance with the notice publication, the requirement of actual notice to the occupants and the owners of the adjoining property under Sections 12 and 13 of R.A. 26 is itself mandatory to vest jurisdiction upon the court in a petition for reconstitution of title and essential in order to allow said court to take the case on its merits. The non-observance of the requirement invalidates the whole reconstitution proceedings in the trial court.[7]
For non-compliance with the actual notice requirement to all other persons who may have interest in the property, in this case the registered owners and/or their heirs, in accordance with Section 13 in relation to Section 12 of RA 26, the trial court did not acquire jurisdiction over L.R.A. Case No. RTC-237-I. The proceedings therein were therefore a nullity and the January 14, 2009 Decision was void.
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