How many brothers did the rich man in Hades want Lazarus to warn?

Answer: Five

He begged for Lazarus to warn his five brothers; Abraham said, "They have Moses and the Prophets; let them listen."

“‘Then I beg you, father,’ he said, ‘send Lazarus to my father’s house, for I have five brothers. Let him warn them, so that they will not also end up in this place of torment.’ But Abraham replied, ‘They have Moses and the Prophets; let your brothers listen to them.’”— Luke 16:27-29 (BSB)