Well, I would be angry too if I had been locked in a cage without proper nutrition and forced to gnaw on myself out of hunger for god knows how long! Obviously that's not the fault of anyone in your family, and you are clearly wanting to help Kenny. However, Kenny has no reason to trust humans in general right now. What kind of trust building activities have you tried so far? Typically, good started activities to gain trust with abused birds would be to sit by the cage and read (or talk) softly to the bird. It doesn't matter what exactly your's reading/saying, it's the soothing tone of voice that familiarizes them with your presence and associates you as an individual as a non-threat. As he becomes more comfortable, you can bring over some favorite foods and eat (or pretend to eat) some then 'share' with him, all while he is still safely in his cage. Whenever he comes near, reward him with a treat. This process can go quickly or slowly, it depends on the bird and they set the pace. Once he starts gaining trust, then you can start working on the issues with being cage bound and quite possibly not knowing how to step up (it happens that some birds have never been taught). Baby steps with these guys. It took several months before our bird was ready to come out and explore and even longer before he was ready to start learning how to step up.
Toys are especially important for aggressive birds and feather chewers, so I'm glad he has some. The toys give them something to occupy themselves, vent their rage on and a distraction from chewing on themselves

Is he playing with or chewing on them at all yet?
And understanding he had an extremely poor diet for some time and years of poor nutrition won't be undone in a few months- What kind of diet is he eating now? Any acceptance of healthy foods like fruits and vegetables? Any luck converting him to pellets or fresh food? Did the vet give any guidelines? Nutrition can play a huge factor in behavior. If the bird is feeling run down and icky all the time due to poor nutrition (amazons are especially prone to these issues, especially if on an all seed diet or eating lots of unhealthy human food), it makes them crabby. And I think just about everyone who's ever rescued a bird knows getting them to eat healthy foods can be extremely difficult, so no judgment on you, just curious how he's progressing diet wise
Just a heads up too- One more thing is expect for his aggression issues (if he is in fact a male) is for the aggression to get worse here shortly. Males (even old ones) get hormonal around this time of year, and even birds who've been in a loving home their entire lives can get perturbed by their 'natural urges'

Aggressive male rescues can backtrack on any progress made and/or may not make any new progress during the breeding season. It usually subsides after a few weeks and is totally normal/healthy.