I ran on that stone making the dual quantums for the TAP defiant. one way to solve it is giving them slightly more turning speed, and less launch speed. also, these torpedoes are meant to be launched at a considerable distance. mine are accurate at about 25/40 km. less or more than that and they either pass the target, or turn too soon.
that's why I equipped that defiant with all three types of weapons. quantums for long range, phasers for medium range and pulse for close combat
another thing: dual tubes (or grouped tubes for that matter) can't be set to skew the torpedoes forward. if the angle of the skewing vector is less than 45 degrees off the perpendicular (or so) to the firing vector, the tube won't fire at all.
although, I think it might be possible to... "compensate" that a bit. from simple maths, if you put two vectors perpendicular to each other, their sum is another vector, at 45? between them. if you set the firing direction to 45? downwards, and the skewing vector of both tubes, 45? upwards (90? to the firing vector) the result might follow the ship's heading at 0?, but I don't remember getting it right, or trying it at all. I sort of "got around" that problem making them skew crossed a few meters beyond the "nose" of the defiant. that left them moving to the target spreading out.