Well, his diet is bad [too high protein, too high fat and no real nutrition] and his light schedule is off so, if he was kept this way before you got him too, he is overly hormonal and, at his age, most likely in constant pain. All birds need to be kept at a strict solar schedule with full exposure [at least 1.5 hours but 2 hours is better] to twilight [this means that there cannot be any artificial lights that can reach the bird before the sun is up in the sky in the morning or after the sun is halfway down to the horizon in the evening]. By simply covering and uncovering his cage, he is not getting the benefit of dawn and dusk and they need it because the different light that happens during these times is the ONLY thing that turns on or off their 'internal clock' which they need in order for their endocrine system [the one that either starts or stops the production of sexual hormones] to be in tune with the seasons. When birds are exposed to a human light schedule [what you are doing right now], they end up overly hormonal and having what people call 'behavioral problems' [biting, screaming, plucking, etc]. Now, the solar schedule changes naturally with the seasons but, this time of the year, I uncover my birds' cage [and open up the blinds in the windows and their cages doors] at 6:15 to 6:30 am, turn on the overhead lights at 8:15 am when I give them their gloop [they get their raw produce at around 7:45 am] and, in the pm, I turn off the lights at 5:30 pm, give them dinner at 6 pm and cover their cages at 7:45 pm. There is no TV, no radio and, if we have to talk, we do in very low voices after they get their dinner so there is complete darkness and quiet to ensure quality sleep for them so, if the bird is in the TV room and there is people in it after 6 pm, he is not getting enough rest even if the cage is covered.
Now, if your father screamed and maybe even swatted at the bird because it was chewing furniture that could have made him distrust all the humans in the household, even the ones that did not do it. You never said if there were children in the house but I might as well tell you that, usually, grays do not do well in households with children or that are too busy in terms of people coming and going, loud TV, etc. Grays are naturally high-strung birds that need a quiet environment and calm people. No screams, no sudden movements, no hullabaloo, etc. just a lot of patience and a soft voice because punishing them or screaming at them doesn't work and only makes things worse [parrots have no bosses in the wild and they don't even understand the concept of obedience or discipline].
Please correct me if I am wrong but it sounds as if you are not really the bird's owner and, if that is the case, I don't know what you can accomplish but the bird needs to be kept at a strict solar schedule with full exposure to dawn and dusk and completely darkness and quiet for sleeping. His wing feathers need to be allowed to grow back because handicapping them is dangerous for them [they have no way of getting away from danger and this makes them terribly insecure and anxious which can translate into aggression]. Furthermore, it's unhealthy for them not to be able to fly as they need flight in order to keep their respiratory system healthy. Rule of thumb is four hours of out-of-cage time but I personally consider this number not anywhere enough for a bird, especially a bird that has no other bird as a companion. He needs a very large cage placed near a window so he can get natural light through it and the cage needs to be tall enough that his roosting perch is at a person's eye level when standing up [prey birds do not like anything or anybody looming over them]. It should also be against a wall but, if this is not doable, a large piece of material should be draped over the back so as to create a fake 'wall' [this reduces stress and anxiety]. He needs to be fed a fresh food diet [something like gloop, mash or chop accompanied by raw produce for breakfast and all day picking] with a measure portion of a good quality seed/nut mix for dinner and a multivitamin/mineral supplement [you might want to start this immediately because if all he has been eating is seeds, he is badly mal-nourished.
Now, there is something in your post that is either incorrect or very alarming [and I do hope for the bird's sake that it's incorrect!] and that is the fact that you say that after 7 months in your home, the bird has not a chosen human because parrots ALWAYS choose a human to bond to. Sometimes, they choose the wrong human [as when they choose a person who is not there for them all the time or doesn't like or know how to treat them properly -like my husband, for example
] but the only time they remain without a chosen human is when they are disaffected and the only way a hand-fed parrot becomes disaffected is when he has been severely neglected for a long time or abused. Is it possible that this bird came from an abusive or severely neglectful situation?
Parrots are VERY high maintenance companion animals - a million times more difficult to keep healthy and happy than dogs or cats because they are avian undomesticated species with complex psychological and physical needs... a cage, water and commercial food don't do it for them. And African Grays are one of the more difficult species because they require a very special environment to thrive, are naturally picky eaters and more prone to behavioral problems than other species so prior parrot experience is almost a pre-requisite with them.