I feed all my snakes ASF and the occasional F/T rat. Nutritionally, there is no difference. If it were me, I would continue to feed them what they eat.

You can keep trying the tough love approach, eventually they should switch, but some ball pythons will get hooked on a certain prey item. It could be rats, mice, gerbils, asf, you name it! It doesn't have as much to do with the prey item as much as it has to do with a picky snake