A Front Hip Circle primarily needs upper body strength to finish with straight arms. It's a swing skill otherwise that is fixed by working the stretch/fold/push parts of the skill.
Press HS:
work lots of HS, shoulder strength. pushups, dips, handstand pushups/shrugs
straddle-L hold
Leg lifts in a HS in straddle and pike.
Back extension roll just needs a strong enough shoulder girdle besides making sure the arms are extended all the way without any slack. Shoulders in ears, shoot toes and legs. Make sure you open and push shoulders as you reach back.