Will orthotics help straighten out my legs?

Yes and No. The bone in the leg will not change shape especially if the bone is mature however, if you are pronating your foot and causing torque on the legs, wearing orthotics may help to realign the foot to the leg and reduce the deformity ie knock knees. So although orthotics can't literally straighten the leg they can help reduce deformity caused by fallen arches and other foot deformities.
No. Orthotic devices can do a variety of things. If you have a symptomatic flexible flat foot orthotics can support your arch, reduce fatigue and decrease pain. Sometimes flat feet can cause knee pain and orthotics can help for that as well. If you have calluses or pressure points orthotics can help relieve pressure. However orthotic devices will not straighten you legs..