Bought property from an auntie, can she be forced by her adopted son (not legally) to take it back?

My auntie (mother side) sold me a 100++sqm piece of land which is half of the total property she has. I processed everything at the BIR, RDA, and Municipal office of San Antonio Zambales. This was just last year. I haven't had it surveyed by a Geodetic engr yet so there was just an additional information attached to the original title about the sale.
Now, my auntie adopted a son long time ago but not legally. This young man, kept nagging and verbally abusing her because he wants the whole property for himself. It seemed that he would forced my auntie to take it back from me. My auntie is a 75 year old single woman and never had a biological child. The young man, threatened to file charges against me. What right does he have? What legal step should I make just to make him stop harassing my auntie about this matter? I don't intend to give it back because the manner that my auntie acquired this property long time ago was I think anomalous as my mother and my uncle didn't know about the transaction that of my auntie and grandmother who's now been dead for a long time. My mother died earlier than my grandfather, so I and my siblings kept mum for quite sometime. My uncle convinced my auntie at least to sell me the other half. This is also with the consent of my siblings. We were the first grandchildren so we did enjoy the ancestral compound in the province no matter how small it is. Can you advice me please? Can I go to the brgy to file a complaint against the young man? And what law covers my situation?

The owner of a thing has the right to enjoy what he wants in his/her property and can not be controlled by third person who has no interest therein. Any complaint or action that the alleged adopted child could files WILL NOT PROSPER being NOT A REAL PARTY IN INTEREST.

Thank you for that clear advice. But again, what if my auntie was convinced by a third party and decided herself to take the property back. Is there a time element after the sale? I haven't gone through the process of dividing the land and getting it titled under my name, yet...

Again, thank you.

One of the things that could really protect you is a deed of sale. This is also required when you wanted to have the title transferred under your name.

Thank you. I acquired insights from you. This venue is really very helpful. Kudos!

The word ABSOLUTE in the Deed of Absolute Sale is CONCLUSIVE AND PERFECTED and cannot be voided or force to back sale by the interference of third party, except the VENDOR is not a sole owner of the property involved.