The estate of late NASCAR legend Greg Biffle is being sued for a total of $30 million following a fatal plane crash that killed seven in December. Biffle, his wife Cristina, their 14-year-old daughter Emma and 5-year-old son Ryder were killed in the crash, while pilot Dennis Dutton, his son Jack Dutton and Craig Wadsworth also perished. Now, the estates of the Duttons have filed separate wrongful death lawsuits worth $15 million each, with the suits claiming that the Cessna C550 plane  —  which was owned by Biffle  —  was not maintained properly. Following the crash, which happened at Statesville Regional Airport in North Carolina, the National Transportation Safety Board (NTSB) said in a preliminary report that Jack Dutton was operating as the co-pilot next to his father. Seven people, including Greg Biffle, were killed in the fatal crash. via REUTERS Biffle.…