The result was unexpectedly strong and makes the younger Bolsonaro the favourite, commentators said.
US President Donald Trump, who has not publicly endorsed either candidate in recent months, called it a "great victory" on Monday. He had earlier demanded the release of Jair Bolsonaro, who was sentenced last year to 27 years in prison for plotting a coup after losing the 2022 election to Lula.
The family also did well in the parliamentary and state votes. The Liberal Party took the most seats in the lower house and will be the biggest group in the Senate. Jair Bolsonaro's wife, brother and two other sons won seats in Congress.
The Economist said the conviction had raised hopes that Brazil could move past nearly a decade of polarisation. "The Bolsonaro clan seems ready to return", the weekly wrote.
Argentina's La Nacion said the movement is now positioned to push its aims. These include an amnesty for Jair Bolsonaro and others involved in the 2022 plot, and the removal of unfriendly Supreme Court judges. "Bolsonarism has consolidated in Congress and is preparing an offensive", the paper wrote.
The New York Times noted that candidates from the right have won seven of the last 18 months' elections in Latin America. It said Brazil, the region's largest country, remains the missing piece among Trump's allies there. A Flavio Bolsonaro victory would change that, it said.
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Source: PAP