The pair are being held on suspicion of human trafficking, rape and sexual assault, which they deny.
Just 24 hours earlier, Romanian authorities launched fresh raids, searching seven homes.
Detectives investigating the claims against Tate had already seized £3.2m worth of assets from his home in Bucharest.
Romanian authorities said 29 assets – including luxury vehicles, watches and cash – had been taken in a raid on his compound in the capital.
On Saturday, several cars, including a Rolls-Royce, BMW and Mercedes-Benz, were taken from his compound on the outskirts of the capital, to be transported to a storage location.
A judge has now ruled the brothers and two others will be kept in prison for a further 30 days while police build their case.
Ramona Bolla, a spokeswoman from Romania’s anti-organised crime agency Diicot, said prosecutors requested a second 30-day extension to keep all four in detention on Thursday.
That request was granted on Friday, Ms Bolla said. The reasons for the extension will be given in a written statement later.
Tate, 36, a British-US citizen who has 4.7 million followers on Twitter, was initially detained in December on charges of being part of an organised crime group, human trafficking and rape.
His brother and two Romanian women are also detained in the same case.
On Tuesday, a court rejected an appeal by Tate against a judge’s earlier decision to extend his arrest from 24 hours to 30 days.
Tate, a former kickboxer and contestant on the reality show Big Brother, gained notoriety for his misogynistic remarks and hate speech.
He was banned from all major social media platforms, although his Twitter account became active again in November after Elon Musk acquired the platform.
His Twitter account has continued to post messages despite his detention.