Sweet potato and yams have a lot of vitamin A and I feed it about once a month as a treat to all my tortoises. I only partially cook it so its a little more firm and gives them something to bite.
You shouldn't need to cook the pumpkin at all. It isn't much harder than squash inside. I just cut it in slices and let them bite pieces off. As Yvonne said, the sweet potato needs to be cooked some to soften it a little.