Georg Thoma, the lawyer, and Paul Achleitner, the financier, worked together for more than two decades modernizing Germany Inc. When Achleitner needed a specialist to solve the multibillion-dollar legal headaches at Deutsche Bank AG, where he was chairman, he turned to Thoma. But now, the 71-year-old attorney has turned on the banker. The conflict has burst into the open, deepening the troubles at the country’s dominant financial institution. Thoma’s intensive inquiries into Achleitner and Deutsche Bank executives have left him isolated, according to at least two board members who have spoken out against him in public. The 20-person supervisory board was scheduled to meet this week and will probably discuss Thoma, who may come under pressure to step down, a person familiar with the matter said.