“For someone concerned about their privacy and public profile, that is a pretty horrible thing to contemplate,” said James Ferguson, a partner at London law firm Boodle Hatfield who specializes in family matters including divorces. “It’s going to incentivize him to want to settle the case.”

David is the older sibling by 10 minutes. Born to Scottish parents, they spent their early days in a west London household so close to a railroad that trains rumbling by would rattle the windows. After leaving school at 16, David and Frederick started their careers in the accounts department of General Electric Co., according to “The Twin Enigma,” a 2010 book by Vivienne Lewin. They teamed up in the 1960s to turn old boarding houses into hotels and moved into breweries and casinos, marking the beginning of their business empire.

When a Middle East oil embargo sparked a collapse in U.K. stocks and real estate during the 1970s, the twins defaulted on loans owed to a British government agency that had expanded into corporate lending. The brothers almost lost everything, but were spared from absorbing the full losses.

The twins have since bought companies that others often reject or overlook, developing real estate and selling off pieces for quick profits. That strategy has allowed the Barclays to own more than 50 firms in the U.K., Japan and Sweden and gain stakes in at least a dozen more.

These include Sears Plc, which once had businesses ranging from women’s wear to mail-order shopping. With financing from Bank of Scotland and Bank of Boston, the Barclays joined with fellow billionaire Philip Green two decades ago to buy the clothing retailer for 548 million pounds. Green and the Barclays recouped the purchase price within 12 months by selling some of Sears’s real estate and its three retailing units.

The Barclays also paid 2.3 million pounds in 1993 for the English Channel island of Brecqhou off the U.K.’s southern coast for a family compound. They erected a mock-Gothic castle, complete with almost 100 rooms, gilded turrets and a helipad. A visitor from the neighboring island of Sark said framed pictures of the brothers with Nelson Mandela, Margaret Thatcher and Charles de Gaulle adorned a palatial living room. The twins would finish each other’s sentences, the visitor said.

Even as their holdings grew, the business has remained a family affair, with David’s sons Aidan and Howard increasingly running matters.

“Our business is large, but is a family business,” Frederick Barclay said in a 2012 witness statement as part of a U.K. court case about their attempts to buy a number of luxury hotels in London. “My brother and I retain a strong interest in the affairs of the business and regularly discuss matters with Aidan and Howard and other advisers.”

But even as the family’s holdings evolve and the younger generation exerts more sway, one tenet remains constant: Discretion is paramount.

--With assistance from Tom Metcalf and Jack Sidders.