Facebook Inc.’s move to change its capital structure was tainted by secret text messages and meddling from financial advisers that pointed to a process rife with conflicts of interest, according to investor lawsuits filed in Delaware.

Late last summer, Chief Executive Mark Zuckerberg asked the board to approve a plan to create a new class of nonvoting shares that would allow him to maintain control of the company he co-founded. The board formed a three-person special committee tasked with assessing the capital plan.

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