What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23)Jumpers left aircraft at 13000FT and deployed drogue parachute successfully. At 5500 ft pulled "drogue release" an nothing happened (this should have deployed main parachute), and drogue was still attached to jumpers. The "cut-away" was pulled and drogue pulled main chute away from jumpers as designed (this is suppose to active reserve, and may have). At same time the reserve handle was pulled. Jumpers rotated to a head down attitude after drogue left. Reserve chute and lines were felt deploying along instructors legs causing "tension nots" and intangled lines. Approximately 1/3 of reserve chute deployed. This cause the jumpers to complete the remainder of fall in what would be called a "flat spin".
As the FAA filed it
(-23)JUMPERS LEFT AIRCRAFT AT 13000FT AND DEPLOYED DROGUE PARACHUTE SUCCESSFULLY. AT 5500 FT PULLED "DROGUE RELEASE" AN NOTHING HAPPENED (THIS SHOULD HAVE DEPLOYED MAIN PARACHUTE), AND DROGUE WAS STILL ATTACHED TO JUMPERS. THE "CUT-AWAY" WAS PULLED AND DROGUE PULLED MAIN CHUTE AWAY FROM JUMPERS AS DESIGNED (THIS IS SUPPOSE TO ACTIVE RESERVE, AND MAY HAVE). AT SAME TIME THE RESERVE HANDLE WAS PULLED. JUMPERS ROTATED TO A HEAD DOWN ATTITUDE AFTER DROGUE LEFT. RESERVE CHUTE AND LINES WERE FELT DEPLOYING ALONG INSTRUCTORS LEGS CAUSING "TENSION NOTS" AND INTANGLED LINES. APPROXIMATELY 1/3 OF RESERVE CHUTE DEPLOYED. THIS CAUSE THE JUMPERS TO COMPLETE THE REMAINDER OF FALL IN WHAT WOULD BE CALLED A "FLAT SPIN".