For camel you also need to have strength in the back. I would recommend buying ankle weights (a set of progressively heavier ones) and wear those when you do spiral positions at home. You can also use a Dynaband and tie one end around one ankle and the other around the other and lift legs into the spiral position. You have to make sure that you tighten your abdominals when you do these.
For the quads you need to do a lot of lunges and one legged squats- that would help a lot with the sit spin.
For both camel and sit you need to make sure that you are not only strong but flexible in your hamstrings. Can you reach the floor with your hands or even better, put them flat on the floor? If not, you really need to stretch those muscles.