He is one of 10 children and three of his other siblings seemed to have not participated.
Grace begins the ad by telling the camera, "Paul Gosar the congressman isn't doing anything to support rural America".
"It's intervention time. And intervention time means that you go to vote, and you go to vote Paul out", says Tim Gosar, a private investigator.
Six siblings of Republican Rep. Paul Gosar delivered a stark message in a new television advertisement: Vote for their brother's opponent.
In a statement regarding the ad, Dr. Brill said the Gosar siblings have always been on record as critical of their brother Paul, but this is the first time they have endorsed a competing candidate or actively involved themselves in a political campaign.
Gosar, a four-term congressman, is a staunch conservative and supporter of President Donald Trump. Brill's team reached out to the Gosar siblings after seeing some of their criticism on social media, according to the Phoenix New Times.
The Republican candidate has previously come under fire for flying to England over the summer to voice support for an extremist anti-Muslim organization. He also believes a conspiracy theory that suggests that the 2017 Charlottesville white supremacist rally was created by liberals. "If you can't speak out against your family, then don't be a hypocrite and speak out against someone else's family member".
"None of this is pleasant for any of us", David Gosar says.
"I couldn't be quiet any longer, nor should any of us be", sister Grace says.
Whether or not speaking out will make much of a difference is up for debate.
Rep. Gosar has held Arizona's 4th district seat in the U.S. House of Representatives since 2013. In 2016, he was re-elected to the job with 71 per cent of the vote.
"This is a matter of right and wrong, not politics", the letter by Gosar's siblings stated. David Gosar told the Arizona Republic, "If (Paul Gosar) had any guts or decency, he would apologize to George Soros on Vice News".
Sister Joan Cosar, an engineer, says, 'I think my brother has traded a lot of the values we had at our kitchen table'.
"This isn't just about Paul".
The next month, Gosar said FBI and Department of Justice officials such as Deputy Attorney General Rod Rosenstein, former acting Attorney General Sally Yates, and former FBI Director James Comey should face "treason" charges due to developments in the Russian Federation investigation.