Directors of the indicted companies had in September pleaded guilty to money laundering but Dudafa and two others
Federal high court judge Babs Kuewumi said the conviction of the property and investment companies -- Pluto, Seagate, Transoceanic and Avalon -- on Wednesday in Lagos came after they pleaded guilty to money laundering in September.
The Economic and Financial Crimes Commission (EFCC) had in July frozen the accounts of the companies and seized $15.5 million (14 million euros) while investigating Waripamo-Owei Dudafa, Jonathan's former domestic assistant, over money laundering.
But then Patience Jonathan, the wife of the former Nigerian leader, sued the EFCC, claiming ownership of the money found in several accounts in local banks.
Jonathan, who has not been charged over the money laundering, said she had been withdrawing the money from the accounts to pay for her overseas health expenses.
Directors of the indicted companies had in September pleaded guilty to money laundering but Dudafa and two others, lawyer Azubike Briggs and banker Adedamola Bolodeoku, pleaded not guilty.
EFCC prosecutor Rotimi Oyedepo asked the court to order that the money be forfeited to the government but that was refused by the judge, who deferred his ruling until the trial of Dudafa and the other suspects, which he adjourned to mid-December.
President Muhammadu Buhari, who defeated Jonathan in the 2015 vote, has launched a wide-ranging campaign against corruption targeting key members of the previous administration.
Former ministers, prominent party chiefs, media owners and relations of the former president are in court over similar charges.
The focus on officials from the former ruling party has led some critics to claim Buhari is using the anti-graft crackdown to silence political foes, an accusation dismissed by the government.