The charges come as Gwent Police said a 60-year-old potential British victim was found in St. Brides, a rural area outside the capital city of Cardiff. A Polish man was discovered at a nearby farm.
Authorities haven't yet determined whether the men were believed to have been held as slaves; a police spokeswoman described them as "potential victims or witnesses."
Prosecutor Catrin Evans said Thomas Doran, Daniel Doran and David Daniel Doran are being charged with false imprisonment, conspiracy to hold a person in servitude and conspiracy to require a person to perform forced or compulsory labor. Thomas Doran also will be charged with kidnapping by fraud, Evans added.
The three will appear in court on Thursday.
Police say their investigation into potential slavery offenses was sparked by the discovery of a missing man who was found living "in very poor conditions" in the area earlier this year. He had disappeared about 13 years ago.
Four other people have been arrested as part of the investigation.