The judge also fined the three $813 each and ordered the cancellation of the allotted plot for Rehana.
There are 14 other suspects.
Khan Mohammed Mainul Hasan, the corruption watchdog’s prosecutor, said they had sought life in prison for the prime defendants.
“We expected life sentences, (but) that did not happen. We will consult with the commission for our next course of action,” he said.
Hours after Monday’s verdict, Hasina’s Awami League party in a statement sent to The Associated Press said the verdict was “entirely predictable," and that the anti-corruption watchdog body “itself is a political mechanism used for political ends.”
“The allegations against Sheikh Hasina, her sister, and many others including members of her immediate and wider family are firmly denied ... The process fails to pass any reasonable test of judicial fairness – a point that has been made forcefully by both local and international legal experts,” the statement said.
The prosecution said Siddiq was tried as a Bangladeshi citizen and authorities said they obtained a passport, her national identity card and tax number. But Siddiq disputed the claim and said she is a British citizen, not a Bangladeshi citizen.
Siddiq, who represents London's Hampstead and Highgate areas in Britain's Parliament, had earlier denied the allegations and said the trial was a farce built on “fabricated accusations and driven by a clear political vendetta.”
In January, Siddiq resigned as a government minister in the Cabinet of Prime Minister Keir Starmer under pressure because of her ties to her aunt. Siddiq had said she had been cleared of wrongdoing but was quitting as economic secretary to the Treasury because the issue was becoming “a distraction from the work of the government.”
Hasan, the prosecutor, said Monday they would reach out to the British government through Bangladesh's Ministry of Foreign Affairs regarding Siddiq's verdict.
Hasina was sentenced to death in November for crimes against humanity involving the crackdown on the mass uprising that ended her 15-year rule last year. She lives in exile in India, and all of her trials have been conducted in absentia.
She and the others in the case decided Monday did not appoint any defense lawyers to represent them.
Rehana is staying outside the country and Siddiq's two siblings are also abroad as they face other charges involving last year's uprising.
In three separate cases involving the same township project, a separate court on Nov. 27 sentenced Hasina to 21 years in jail. Hasina's son and daughter were also sentenced to five years in jail each by the court in that case.
The country is now run by an interim government headed by Nobel Peace Prize laureate Muhammad Yunus who declared the next parliamentary election will be held in February.