I think you get most from hanging leg raises from high bar. It work lot of muscles for stability like obliques and seratus and more, grip strenght and endurance but you can stick with parallel bar leg raises. After your stabilisation muscles get stronger with hanging knee raises you can switch from parallel to normal bar.
Windshield wipers is one of the hardest abs excercise. You need get good at hanging leg raises, then try go higher with legs to touch bar with your foot (your back will curve if you raise legs higher than parallel with floor). As a preparation to windshield wipers you can do them on floor, then you can try hanging windshield wipers with bent knees and then straightening legs as you get stronger and confortable with it. L-sit/hold may also help you too.