Emily Post Family -- Bitch Fight Over Kardashian Wedding Gifts

Emily Post literally wrote the book on proper wedding etiquette ... but now, her famous descendants are butting heads on what Kim Kardashian should do with her wedding gifts.

On one side, Emily's great-granddaughter-in-law Peggy Post -- who wrote an article in The New York Times just three months ago, explaining how gifts should be returned if the wedding is canceled, or if the couple "seeks to end the marriage almost immediately (say within a month or two)."

Since Kim and Kris just inched past the two month mark ... they're in the clear with Peggy.

But on the other side of the etiquette battle is Emily's great-great-granddaughter, Lizzie Post -- who told the New York Daily News, "after just 72 days, the gifts must be returned to the wedding guests."

As we previously reported, Kim is not returning the gifts -- instead, she's making a $200k donation to her favorite charity.

Sources close to Kim tell us ... KK feels the gifts were given out of love and she doesn't feel an obligation to return them to the sender. But we're told Kim understands her marriage was short, and decided the donation was a good compromise.