Ike Ekweremadu, 60, his wife Beatrice, 56, and a doctor, Obinna Obeta, 50, were found guilty at the Central Criminal Court, the Old Bailey, of conspiracy to arrange the travel of another person with a view to exploitation, under UK legislation on modern slavery.
The kidney was allegedly intended for Sonia, who remains on dialysis with a renal condition, in return for up to £7,000 ($8,430) and the promise of a new life in Britain for the 21-year-old trader.
The prosecutor earlier said the young man had been coached to give false answers to doctors at the British hospital, and Sonia was "singing from the same hymn sheet" to create a fake family history linking the pair as cousins.
Obeta allegedly managed the process in Nigeria, having himself undergone a kidney transplant in Britain with an organ donated by a "cousin" in 2021, the court was previously told.
In Britain, it is legal to donate a kidney, but not for reward. Prosecutors say regardless of whether the Lagos street trader gave his consent, a crime was committed by the wealthy Nigerians.