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The Hardy Brothers are in a nasty family feud -- with Jeff not only trashing his brother Matt ... but also going after his wife, calling her a "witch bitch" who's tearing the family apart.

It all went down on the "TMZ Sports" TV show -- when the wrestling superstars were talking some serious smack to each other leading up to their "I Quit" match on TNA Impact Wrestling Tuesday on Pop TV.

It started off with the usual threats ... but got crazy personal when Jeff brought up Matt's wife ... calling her a "witch bitch that's casting spells" who's turning the brothers against each other.

Matt fired back -- warning him about going after his wife ... and promising to "make [Jeff] suffer" when they face off tomorrow on Pop TV.