What Assist in flexing and rotation of hip and flexion of the knee?

If you are looking for the answer of what assists all of those movements at the same time, the answer would be the Gluteus Medius and Minimus muscles. Think of a squat, while you are squatting both your hip and knee are flexed (the gluteus medius and minimus are the stabilizers/assisters during a squat), and while the hip is flexed the gluteus medius can internally rotate the thigh.