Rep. John Conyers’ resignation Tuesday has set off a family feud as to which relative will replace the longest-serving member of the House.

Conyers, 88, announced he supports his oldest son, John Conyers III, 27. But the Detroit congressman’s grand-nephew, Ian Conyers, 29, also wants the job.

“The difference between the son and the grand-nephew is the fact that Ian is actually an elected senator in the state of Michigan,” said pollster Ed Sarpolus, executive director of consulting firm Target Insyght. “His son, John, has always expressed interest in replacing his dad, and he’s made it publicly known on many occasions even before Ian came onto the scene. There’s no way that John Conyers would be able to say no to his son.”

Complicating matters is that Conyers never intended to retire, and former staffers told The Post he wanted to die in office.

Mounting allegations of sexual harassment forced him to announce his sudden “retirement” and set off a scramble to pass the torch.

Conyers’ son has never held elected office and sparked a congressional ethics stir in 2010 when he was caught driving his dad’s taxpayer-funded Cadillac Escalade. The elder Conyers had to repay the US Treasury $5,682 for misusing taxpayer dollars.

Conyers’ 13th congressional district is heavily Democratic.

Other potential Democratic contenders are Wayne County Sheriff Benny Napoleon, Detroit City Council President Brenda Jones, state Sens. David Knezek and Coleman Young II, former state Rep. Rashida Tlaib and Westland Mayor Bill Wild.

Sarpolus, who served as Conyers’ campaign manager in 2012, said the retiring congressman doesn’t have the funds to propel his son into office.

“John Conyers financially is broke, so there’s really no money he’s going to be able to supply,” Sarpolus said. “I don’t see where John has any political leverage financially.”