Mark and David Wellstone said Thursday that they feel angry, saddened and betrayed by a public dispute with Wellstone Action, the nonprofit created in honor of their father, the late U.S. Sen. Paul Wellstone.

The brothers will be voted off the group's board on Friday, according to David Wellstone and confirmed by media representatives for the remaining board members.

A split in the board's leadership became public Wednesday when the organization announced that it had decided to sever its relationship with the brothers. Three other board members have also left the organization in recent months, after raising questions about its finances that they say are still unanswered.

Now, David and Mark Wellstone said, they want their family name to be removed from Wellstone Action, which trains candidates, political operatives and volunteers in sessions in Minnesota and around the country. Paul Wellstone, who was elected in 1990, has long been revered by many in the Minnesota DFL. He died in a 2002 plane crash.

"At this point, I feel such a deep personal sense of betrayal that it's difficult to lay out what my goals are … other than I know that my brother and I want to get our name back," Mark Wellstone said.

"I'm going to be adamant about getting my name back," David Wellstone said in a separate interview Thursday. In a statement Thursday, the board said that "our goal was never to keep their name."

Until Wednesday when the conflict became public, David Wellstone said, he thought an agreement had been worked out for Wellstone Action to "re-brand" and change its name by the end of the year. That plan included the siblings' resignations.

Mark Wellstone also said he thought that a "fair, amicable resolution" to their differences had been worked out. "And then the carpet was pulled out from underneath us," he said.

After negotiating for months, the board said in its response Thursday, "we had to make the difficult decision to move past this moment." In that statement, the board did not deny that the siblings were blindsided by the announcement of the split.

"From our perspective, we didn't see a willingness on their part to get this resolved in a reasonable or timely way," the board's statement said. "Months of negotiation take their toll on an organization, in time and expense and distraction from our important work."

"I'm furious. I'm shocked. This brings up all kinds of emotions, but particularly emotions of betrayal," said David Wellstone, who provides women's sober housing in Northfield, Minn.

The Wellstones took issue with a statement released Wednesday by the board, which includes co-founder Jeff Blodgett, a longtime political adviser to Paul Wellstone. It said that the brothers, along with now-former board members Rick Kahn and Ron DeHarpporte, had "taken actions in the past year that indicate that they don't support the long-term vision of the organization."

Mark Wellstone said that his "biggest mistake was trusting people who I really felt had our best intentions at heart — people who were at one point close to our family."

His brother added, "They turned this into a war when it didn't have to be."

Kahn, the organization's longtime treasurer, said the trouble began when he contacted the board with a question about $200,000 in spending and a sharp decline in the cash balance.

Both Wellstones on Thursday described that episode as the beginning of the rupture.

In response to Kahn's assertion, Blodgett on Wednesday released a Feb. 2 letter describing a forensic audit the board commissioned from Eide Bailly, a Minneapolis accounting firm. It stated that the audit "found no evidence of any improper payments."

Kahn on Thursday shared with the Star Tribune an Oct. 22, 2017, letter to the board from then-member Louis Frillman. In it, Frillman submitted his immediate resignation "in light of the financial questions that have been raised, and remain unanswered." Frillman is chairman of a Minneapolis investment firm and a major donor and fundraiser for Democrats.

David Wellstone said that he also had broached the possibility of Wellstone Action taking a broader political role in the wake of President Donald Trump's election.

He said he asked the organization's leadership, "What should we be trying to do after the Trump election to get back" some of the voters who supported him? "The answer," he said, "was we're going to throw you off the board."

Mark Wellstone, who runs a small business in Steamboat Springs, Colo., said an end to the family's relationship with Wellstone Action will not damage his parents' legacy.

"I would hope that their legacy is much larger and much bigger than Wellstone Action," he said. "For me, that's just a small piece of their legacy."

His brother agreed. "My folks' legacy is huge," David Wellstone said, adding that he is considering launching a new effort to honor and perpetuate it. "We're going to keep every option on the table."