For me doing them on home made PVC parallets and positioning the parallets quite close together allows me to dig my elbows into my abdominal area and really concentrate my power down through my core. A wide grip is a lot harder to hold a pose.
As for straightening, do you mean your legs? Getting your legs fully straight takes practice and time if your are a newcomer. Hold some frog legged levers for as you can, increasing your core strength and slowly work up to extending your legs fully. Be patient.