Police searched the home and offices of Oleguer Pujol, youngest son of Jordi Pujol, a former regional president and figurehead of the Catalan independence movement.
The investigation into allegations of money-laundering and tax-dodging by Oleguer Pujol is the fourth court case launched against the powerful family in recent months.
The cases have complicated efforts by Catalan leaders to hold a vote on whether their region should be independent from Spain -- a plan that has placed them in a tense standoff with Madrid.
A judicial source confirmed separately that one of them was Oleguer Pujol and the other was his business associate Luis Iglesias.
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Oleguer Pujol is accused of laundering billions of euros in suspect real estate transactions.
The prosecutors added that police also searched properties in several cities.
Jordi Pujol headed the regional government of Catalonia from 1980 to 2003 and became a leading figure in the drive for independence for the rich northeastern region.
Two of his other sons are also under investigation for corruption and influence-trafficking, including Oriol Pujol who stepped down as leader of the Catalan nationalist CDC party last year.
In September the other brother, Jordi Pujol Ferrusola, went before a judge and denied accusations that he earned millions of euros on government contracts and hid the money abroad.