Two of Nelson Mandela's daughters have launched a legal move to oust his close friend and lawyer from the boards of two companies, hinting at ugly power struggles to come over the former president's wealth.

Makaziwe Mandela and Zenani Mandela-Dlamini filed papers seeking to remove George Bizos from the boards of two Mandela-related investment funds.

Bizos, a renowned human rights lawyer, defended Mandela against a possible death penalty in 1964 and made a small contribution to his celebrated "I am prepared to die" statement from the dock.

The court battle looks set to shine an unflattering light on the Mandela family's financial dealings and on potential future conflicts over the anti-apartheid hero's inheritance.

Makaziwe, founder of the House of Mandela wine label, and Zenani, the South African ambassador to Argentina, reportedly filed the legal papers two days after their father was discharged from hospital, where he was being treated for pneumonia.

They have asked the court to oust Bizos, cabinet minister Tokyo Sexwale and Mandela's ex-lawyer, Bally Chuene, alleging that all three forced themselves on to the boards of the two companies worth around 15m rand (£1.1m).

Makaziwe and Zenani claim that the three were never appointed as shareholders or directors of Harmonieux Investment Holdings and Magnifique Investment Holdings.

The two companies were set up to channel proceeds from the sale of Mandela's handprints for his benefit and those of his children. The prized handprint, said to have been accidentally created while working on a sketch inspired by his imprisonment on Robben Island, contains an image resembling the African continent.

Makaziwe said in the filing that neither she nor Zenani "in our capacity as directors, or in any other capacity, have ever received any notice to pass a resolution appointing, or have ever appointed" the three people as directors, South Africa's Star newspaper reported. The three have ignored a request for them to leave the company, she added. According to the Star, the court papers lodged by Makaziwe and Zenani are fiercely critical of the three men, especially Chuene, claiming that he was "criminally conducting himself" when he allegedly appointed himself as director of the companies.

Makaziwe's affidavit alleges that Bizos was "quite happy to participate in this unlawful conduct, as is evident from his acceptance of the sham directorship".

Bizos, 84, who is currently representing victims of the Marikana mine massacre, strongly rejected the claims. "There is no basis to the allegations," he told the Star. "We are not hijackers. We don't hijack things. The public should ask themselves why five years later these allegations are being laid. We are confident we were regularly appointed at the wish of Mr Mandela five years ago."

He added that Makaziwe and Zenani had brought the court application "in order to further their interests and get their hands on the money".

On Wednesday Bizos, who has known Mandela for 65 years, declined to comment further except to say: "Of course I am hurt."

Both companies were established by Mandela's controversial former lawyer Ismail Ayob. A legal statement on behalf of Bizos, Chuene and Sexwale claimed that when Mandela ended his professional relationship with Ayob in 2004 he provided "explicit instructions" identifying who was to be appointed to the companies.

"Our clients were identified by Mr Mandela and were in due course lawfully appointed as directors of the companies referred to in the application," said Michael Hart, a lawyer with Norton Rose South Africa. "We are instructed to record our clients' complete rejection of the scurrilous allegations made by the applicants in their papers. These will be refuted in the answering affidavits filed in support of their opposition to the application."

In an apparent reference to 94-year-old Mandela's failing health, the statement concluded: "Our clients record their dismay at the insensitivity of the applicants in publicly releasing the unanswered court documents, particularly at this time. They will deal fully with the matter in their papers to be filed in terms of the rules of court."

Sexwale, the human settlements minister in the South African government, told South Africa's eNews Channel Africa that he felt there was something "dodgy" about the court case.

He maintained that the three people in question were appointed trustees by Mandela. "I still do not know what the quarrel is about. As a colleague and a comrade of Nelson Mandela, if he appoints you, you do the job."

Sources close to the case told the Guardian that the case had divided the Mandela family, with some members refusing to back Makaziwe and Zenani. A spokeswoman for Mandela's ex-wife, Winnie Madikizela-Mandela, was unavailable for comment.

Mandela has married three times and fathered six children, three of whom have died. His surviving children are all women: Makaziwe, by his first wife, Evelyn Mase, and Zenani and Zindzi, by his second wife, Winnie. He divorced Winnie in 1996 and is now married to Graça Machel.

According to the Nelson Mandela Centre of Memory, he currently has 17 grandchildren and 14 great-grandchildren. It is often speculated that cracks will appear when the family patriarch is gone.