"I hope they find peace in their hearts and let go all the hate", Gosar said.
Gosar, who has been in office since 2013, has made headlines for his controversial actions. Earlier this year, he called for authorities to check the immigration status of those attending the State of the Union address, and arresting and deporting "any illegal aliens attempting to go through security".
"We gotta stand up for our good name", brother David says in the ad.
Brill will face Rep. Gosar in the November general election on Nov. 6.
In an October 2017 interview with the Phoenix New Times, David Gosar had harsher words for his politician brother, scolding him at the time for amplifying conspiracy theories about the white-supremacist rally that year in Charlottesville, Virginia.
In response to the ad, Gosar told CNN in a statement Saturday that the siblings featured in the ad are "liberal Democrats who hate President Trump" and slammed Bill for engaging "in this shameful attack".
"It's intervention time", he said, "when you go to vote, you go to vote...to vote Paul out". His brother Pete, a Democrat who did not participate in the Brill campaign videos, ran unsuccessfully for Wyoming governor in 2014.
Brill told the newspaper that while Paul's siblings are 'really upstanding, wonderful people, ' he has not yet met them and was not involved in the making of the ads so that he would not influence their testimonials.
Bernadette said that she has a "wonderful" family but that the members of the family don't always see eye to eye politically.
To give their endorsement more impact, the ad doesn't name the six speakers until the end.
David Gosar said that Paul Gosar's politics have caused a strain in the family, which hails from the small town of Pinedale, Wyoming.
The Phoenix New Times reported that the ad and others were unveiled at a fundraiser in Phoenix on Thursday night - and that in another spot, which is not public yet, Grace Goser says that "it would be hard to see my brother as anything but a racist".
In a second video, called "A Family Defends Its Honor", the siblings say that speaking up against their brother is personally hard, but they feel compelled to stand up for what is right. "None of us even want to do it", David said.