claiming rights

Dear Sir, Around 20 over years ago, I and my wife (Thai National) bought a piece of land We went thru the Land authority of Udon Thani to complete the process of purchasing. (which is under her name now.) As stated on the bottom of land titles, the adjunction of the land is under our Possession/Care.(unnamed land) around 1 rai. Recently, the previous owner's family come forward to claim that the unnamed land belongs to her as it's passed down from their ancestor. Pls, advise of the path forward. Why didn't they come forward till recently/ What rights do they have? What should we do as we're both staying abroad? Do we need to travel back to Thailand to settle it