Silver Saddle

The film opens in a small South Texas bordertown in the 1850s. A poor farmer and his young son arrive into the settlement where the farmer confronts Luke, a thieving henchman employed by wealthy land baron Richard Barrett. The man complains to Fletcher that he had been cheated by Barrett claiming he had been sold a deed to non-existent property. Fletcher finally shoots the farmer, killing the man in front of his young son. His son then picks up his father's shotgun, uses it to kill Fletcher, and rides out of town with Fletcher's horse and a distinctive silver-trimmed saddle.
The boy is next seen several years later and has since become a hardened bounty hunter calling himself Roy Blood (Giuliano Gemma). He meets an elderly drifter, Two-Strike Snake (Geoffrey Lewis), who accompanies him to the frontier town of Cerriotts. Snake is a colorful character who claims that the story of the "silver saddle" and the boy who avenged his father's death is well known and that he wishes to join Blood in his travels. On the way, Snake often scavenges the remains of those killed in gunfights by Roy Blood.
Their arrival in Cerriotts is noticed by several townspeople, in particular, a local cowboy known as Turner (Gianni De Luigi). Blood visits the town whorehouse where he meets with an old girlfriend, Shiba (Licinia Lentini), who is also its madam. She tells Blood that she is being extorted by a man called Shep who collects the money on behalf of a Mexican bandit named Garrincha (Aldo Sambrell). Shiba enlists Blood's help in taking care of Garrincha and his gang. Indeed, Blood confronts and kills Shep and several of Garrincha's men in a gunfight. Afterwards, Turner appears to offer Blood $2,000 to kill a man called Barrett. Blood is hesitant to take the murder contract, but accepts the offer upon recognizing the name of the land baron who had swindled his father years before.
The murder is arraigned to take place in a graveyard outside town where Barrett is expected to arrive. Blood lies in wait until a carriage eventually pulls up. Its occupant is a young boy however, not the older land baron he had expected, who enters the graveyard carrying a funeral wreath. Blood then sees several men who ambush the child, but before they can kill him, Blood shoots the assassins and rides off with the boy. Blood learns the boy's name is Thomas Barrett, Jr. (Sven Valsecchi), the son of his intended victim Richard Barrett. The elder Barrett has been dead for several years and Thomas, Jr. has since been cared for by his uncle Thomas Barrett, Sr. (Ettore Manni). Angered at being cheated out of his revenge, Blood leaves the boy stranded in the hillside with only a knife and blanket.
Back at the Barrett homestead, the Thomas's older sister Margaret (Cinzia Monreale) is upset over her brother's disappearance. Thomas, Sr. discusses the search with Turner, who is revealed to be the ranch foreman, and is decided by the land baron that Roy Blood is the kidnapper and posts a $5,000 bounty. Meanwhile, Blood is rejoined by Snake who offers him a deal. Snake reveals that he took in Thomas, Jr. after he left and intends to ransom the boy back to the Barrett family. Blood is also informed that the bounty was a ploy used to kill himself and the boy, with Blood being blamed for the murder.
Blood hides out at Shiba's whorehouse, and where Thomas, Jr. is looked after, while Shiba obtains information on the Barrett family. Using her feminine wiles, she is able to learn that after the death of Richard Barrett, his fortune was divided between his children and his brother. However, Thomas gambled away his half of the inheritance while the family fortune was possessed by his children. The will provided that if Thomas, Jr. died, Margaret would inherit the entire fortune. It is presumed that is the motivating factor for Thomas Barrett, Sr. to marry his niece.
Thomas, Jr. is eventually spotted by Turner while visiting the whorehouse and Blood takes him to the San Jacinto monastery located several miles away. The gun-toting padre of the monastery promises to protect the boy while Blood goes after Turner. He eventually confronts Turner and his men at an abandoned farmhouse where a shootout occurs and Blood kills Turner. But at the monastery, the bandit Garrincha and his gang have killed all the priests and taken Thomas, Jr. whom they plan to ransom for themselves. Blood is later arrested by the sheriff (Phillppe Hersent) who believes he is a member of Garrincha's band.
The bandit leader demands $10,000 for the safe return of the boy. Thomas, Sr., against the advice of the sheriff, agrees to pay the ransom and sends out a messenger named Fletcher (Donald O'Brien) to deliver the money to Garrincha's camp. The courier is murdered once he hands the money to the bandits.
With the help of Margaret, Blood eventually escapes from the town jail and reunites with Snake to track down Garrincha. They finally find the bandit's hideout when Thomas, Jr. flies a kite over its location. Blood and Snake arrive to find Garrincha whipping the boy after discovering his ruse. A gun battle with Garrincha and his men results in the death of the bandit, but not before Snake is killed.
Blood returns to the Barrett ranch with Thomas, Jr. and exposes his uncle's role in the kidnapping revealing that Thomas, Sr. had planned with Turner to kill his niece and nephew so that he would gain the family inheritance. Garrincha was also part of the plan, Thomas, Sr. staging a false kidnapping and ransom payment to avert suspicion from himself, and had intended to kill Turner as well as Margaret once he married her. Blood kills Thomas, Sr. with one of his ornamental pistols. The film's conclusion shows Blood riding out of town with Thomas, Jr. alongside him.

Question: With whom did Thomas, Sr. plot to kill his niece and nephew?
Answer: Turner and Garrincha