How can we contest Actual Occupancy, Land development and Tax declaration?

Good day Sir/Madam. I'm pretty desperate where to find free legal advice until I type my question that led to this site. Our family is also having a problem with regards to hectares of land in Baguio City and la Trinidad Benguet. The said land belonged to my ancestors (we belong to Ibaloi tribe). For hundred of years, it had been developed by my ancestors until the laws had been very strict when it comes to titles and taxes. The title of the land was named before the grandparents of my mother in 1967. My parents and their siblings had been paying for tax declaration until now when a person claiming to be a representative with SPA came, saying that a certain person in the name of Juanico O. bought land in 1961 with his deed of sale. I had research to the registry of deeds that it had been really filed to that Juanico O. We had tried to settle it in the level of DENR in our barangay but the hearing officer is obviously intimidated. When it comes to papers and documents, I would like to know how to make their deed of sale invalid for the fact that all of those signatories are all dead.we never saw that Juanico personally in all years of the barangay hearings. Only the SPA representatives come to the hearing. I would like to ask also the jurisdiction of DENR over this matter.Can the municipality still issue me a building permit to allow me to build a house using the tax declaration? What are the legality of having an SPA fighting in all that hearings and how can we counter it? We know that it will be more harder to go on trial because of financial requirements but would it be much better?

what does the deed of sale say? that your great grandparents sold the property to them?

The 26 heactares of land belong to my great grandmother. The said 6 hectares was given to my grandmother with a deed of sale, surveyed separately in order to ensure that it will be given to her. The history of the 20 hectares had been given to the other Ibaloi people who helped in developing it since time immemorial. Its just been last 2008 when a representative with SPA came claiming that a certain Juanico B. bought the 26 hectares in 1961. The deed of sale was between Juanico B and my great grandmother's brother.