Ike Ekweremadu, 60, his wife Beatrice, 56, daughter Sonia, 25, and a doctor, Obinna Obeta, 50, are accused of conspiring to exploit a man for his kidney.
The Ekweremadus and the doctor are accused of conspiracy to arrange the travel of another person with a view to exploitation, under UK legislation on modern slavery.
Lawyers for the four previously told the trial at London's central criminal court, also known as the Old Bailey, the alleged victim was acting "altruistically."
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.
Giving evidence in his defense, Ike Ekweremadu was asked about an invoice for £8,000 he received via his brother Diwe from a consultant doctor.
Defense lawyer Martin Hicks asked: "Why not at this stage say we are being scammed Dr. Obeta, end of, stop?"
"My daughter's life was on the line so if we stop we will be putting my daughter's life in danger. So we just keep moving," Ekweremadu replied.
"Everybody was obviously taking advantage of my daughter's ill health," he added.
Ike Ekweremadu is a senator for the opposition Peoples Democratic Party for Enugu state in southeast Nigeria. He has been held in custody in the UK since his arrest. His wife and daughter are on conditional bail.
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.
The accuser - who cannot be named - is said to have gone to UK police after finally refusing to consent to the procedure, following preliminary tests at a north London hospital in February 2022.
- 'Scary' condition -
A consultant doctor at the London hospital said the young man had "limited understanding" of why he was there and was "visibly relieved" on being told the transplant would not go ahead, prosecutor Hugh Davies said.
Ike Ekweremadu told the court on Monday Sonia was doing a masters degree at Newcastle University when she started experiencing "swollen limbs" in December 2019.
She was later diagnosed with a "kidney issue", which caused her "distress", and withdrew from her studies after she "collapsed" in class.
Ekweremadu said his daughter's deteriorating condition was "scary", adding: "Medicines she was getting (were) not essentially working, so her situation was getting worse."
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.