The move comes at a sensitive time as the Saudi Government deals with falling oil prices and limits access to Islam's holiest sites over Covid-19 fears. Bloomberg reports that the Saudis have aggressive plans to increase oil output in a price war.
The attempt to consolidate power has led to unconfirmed speculation about the health of the King, although a source told AFP that Salman "is healthy and fine".
The Wall Street Journal reported that, like a scene ripped from the pages of A Game of Thrones, guards arrived at the homes of the princes wearing masks and dressed in black.
"The arrests cast aside two men who could have been rivals to MBS's claim to the throne if King Salman died or decided to abdicate. MBN had been first in line for the throne as Salman's crown prince until 2017, when MBS was elevated over him," the Journal reported.
"It looks like MBS is just taking out all rivals," Michael Stephens of the Royal United Services Institute told the New York Times.
The Crown Prince, who controls the Saudi military, internal security forces and the national guard, has form when it comes to family purges. In 2017 he ordered hundreds of royals and businessmen detained in Riyadh's Ritz-Carlton hotel – presenting it as a crackdown on corruption. He demanded that they turn over large sums of money.
It's another example of how in a kingdom that is run like a sprawling family business, nobody with royal connections is safe.
MBS has overseen reforms in his country that have allowed women to drive and eased regulations that have resulted in new movie theatres and festivals. But he has also been criticised for harsh treatment of female activists.
MBS is most infamous in the West for his alleged role in the killing of Saudi dissident and journalist Jamal Khashoggi at a consulate in Istanbul, Turkey, in 2018.
But he also launched a military intervention in Yemen five years ago. More than 100,000 people are estimated to have died from the war.
The Crown Prince's previous scandals have clearly left him unchastened, secure in the support of the US Trump Administration and guaranteed a welcome at the top table from other wealthy nations.
Meanwhile, the lines of family and public power have become blurred in some high-profile cases of princes-in-all-but-name. US President Donald Trump's daughter and son-in-law are advisers. The son of Brazilian President Jair Bolsonaro, who met Trump at his Mar-a-Lago resort at the weekend, is an aide to his father.
"Prince Mohammed is emboldened - he has already ousted any threats to his rise and jailed or murdered critics of his regime without any repercussion," Becca Wasser, an analyst at the Rand Corporation told AFP.
"This is a further step to shore up his power and a message to anyone - including royals - not to cross him."
