I'm no expert on DP's but if I understand you correctly all of the rockets fire properly, it's just that after the upper ones fire the lower ones seem to be dangling in mid-air not attached to their hangers.

I've not had that exact problem but I have had rockets and bombs that were floating in mid air, even though DPED showed them as being adjacent to their racks.  I've solved that by dragging their hardpoints (using DPED) until they lined up properly.  In some cases DPED showed the ordinance above the rack (in the wireframe window) when in fact they displayed in the game below the rack in their proper position.  Trial and error got them into the correct spot.

You know that you don't have to exit the game to make changes to the DP file.   You can start CFS2 and DPED and have both programs running simultaneously. Go into Free Fliight, select your plane and check the positions of the rockets.  Minimize CFS2 and open that plane's DP file in DPED.  Make your adjustments using DPED.  To view them in the game, open the plane's AIRCRAFT folder and delete the CDP file.  Then maximize the game again, quit Free Flight and go back to the Home Page, Reselect Free Flight, reselect your plane and you can check the changes.  By exiting Free Fight then reentering it the game picks up the new (modified) DP file and you can check your adjustments.  This saves lots of time.  Just remember that you must delete the CDP file after each modification before maximizing CFS2 and reselecting your plane.

Maybe someone else has a thought on your specific problem.

Now that you posted your Mossie I was able to see exactly what the problem was.  I modified your DP file so that it fires the bottom rockets first then the top.  At least they no longer dangle in mid air.  Also the drop tanks now release in that same loadout.  The bombs would drop but not the tanks on the one I downloaded.  I will email you the fixed DP.