Land Property and forging of signature

Hi. I would just like to ask for a legal advice on this matter. My great-grandfather and his 3 brothers are sharing a 2500sqm agricultural land. Even without title, they have been sharing and dividing the produce of the land into four even when two of the brothers died. When my great-grandfather died, my lola (eldest daughter) kept the blueprint and continue to pay taxes and share the produce. Her cousin (son of the living brother) borrowed the blueprint and due to trust, she gave it. In 2017, we found out that the land has been named under the cousin’s name and produce is not being divided anymore. When my lola went to the barangay, they found a letter, authorizing a third person to transfer, cancel and file the old tax declaration to a new one. The letter was dated 2012 with the signature of the 4 brothers as the owner. My great-grandfather died in 1997 and the two other brother died before him. The living brother who signed that document died 3yrs ago. Now, we just want the share of our land. What should be our first step? We also want the forgery to be filed against them. It's clear that they don’t want to give the land as they filed a complaint against us for “paninirang puri” as we are accusing them of stealing the land. What can be our counter to them?

If the forgery can be proven, then you can file a criminal case of falsification and a civil case for reversion.

Just a follow up question, they want to file a case against us for oral defamation for accusing them of stealing. I have read somewhere that if there is a basis and can be proven its not defamation. would our file for forgery and proven true, suffice to dismiss the oral defamation filed against us?

it can be a valid defense