"It would be hard to see my brother as anything but a racist", Mr Gosar's sister Grace tells voters in another upcoming advert, according to The Phoenix New Times.
Phoenix Republican Congressman Paul Gosar's brothers and sisters have made their sibling rivalry political.
It is not the first time the Gosar family's political disagreements have spilled out in the open.
"None of this is pleasant for any of us", David Gosar says. "To speak out against my brother, it brings sadness to me", says Joan Gosar. I hope they find peace in their hearts and let go all the hate.
"If he actually cared about people in rural Arizona, I bet he'd be fighting for Social Security, for better access to health care", says Jennifer, a medical interpreter.
But the sharply personal ad is certain to generate attention for Brill's campaign. Gosar issued a statement in January urging Attorney General Jeff Sessions to check IDs at the State of the Union address and arrest and deport all Dreamers if they attended.
Jennifer Gosar talks about her brother Paul in an advertisement for his opponent David Brill.
Gosar suggested in an interview with Vice News that the rally was "created by the left" and carried out by an "Obama sympathizer". He then branded Democratic Party donor George Soros a Nazi collaborator in an interview with Vice News.
In July, Gosar spoke in London at a rally for an anti-Muslim activist.
'We are aghast that Paul has sunk so low that he now spews the most despicable slander against an 87-year-old man without a shred of proof, and then doesn't even have the guts or decency to apologize? "Those aren't our family values or the values of the small Wyoming town we grew up in".
"It's intervention time", he said, "when you go to vote, you go to vote...to vote Paul out". Brother Pete, who ran for governor of Wyoming in 2014 as a Democrat, does not appear in the ads.
Gosar, a four-term incumbent running for re-election in northeastern Arizona, is a vociferous supporter of President Trump and a conservative hardliner.
Paul, an outspoken Donald Trump fan, won his district with 71 percent of the vote in 2016.
In another spot, the Gosar clan discusses how hard (but necessary) it is for them to join forces against their brother.
"You can't pick your family", Congressman Gosar tweeted.