No. I advice you to get the service of a lawyer to make that document for you. You cannot get it in a city hall/munisipyo. The lawyer is the one who have the knowledge to do that, they have formats. What you need to do is to provide the lawyer the details of the property (like the copy of a title and proof of relationship between the decedents and the heirs) because the lawyer will placed that details in the Extrajucial Settlement of Estate. If you have a time, try to search from the net the sample of the document for you to have an idea.
The SPA is a document wherein you appoint, permit or authorize your attorney-in-fact/agent to perform necessary acts in your behalf. Maybe your buyer need the SPA for the transfer of title purposes. The TIN nos. of the principal/seller are needed to put in the SPA.
Note: I am not a lawyer, im just sharing my knowldge and experience as a real estate specialist.