My son 3y old, still is not able to walk

My son was diagnosed as a child who has DDH bilateral, since birth, also he has have muscle weakness and generalized joints lose (hyper flexable) and flat feet (feet arcus are less), and following treatment procedures has been done: - Pavlik harness for first six month of his life, and was not effective. - spica cast for 2 times, every times for 45 days. and was effective and than the orthopedic center in Kabul, Afghanistan put him in abduction brace for next 3 months, and X_ ray done, showed it was treated. - when he got 2 years old he still was not able to walk, and X-ray done again, showed that the hip joint were dislocated again. note: -he is twin, -he had phemosis and treated by circumcision. -he had un-descended right tested and treated by surgery.