A stern No works very well if they are focused on you. A stern No works well with a trained bird. Much like toddlers, Toos can become overstimulated very quickly. Ely is in a strange new world with strange new people. Two weeks is nothing to a Too. He came to you with baggage and no boundaries. That's okay, you said you were up for a challenge, with the right attitude you can only go forward. A Too's beak has three prongs and as you know they can deliver a very nasty bite, just like the screaming, Ely has been rewarded for biting, a wicked bite gets a dramatic reaction, Toos love drama. Don't pretend the bite didn't happen, he knows very well that he bit you, he attacked you in fact. If possible, avoid situations that cause confrontation. For instance, if your Too is hostile or extremely hormonal, avoid physical interaction. Place him on a stand with a cord of wood, talk to him, visit with him, don't pick him up. A lot of it is action and reaction, with any parrot, maybe more so with Toos. Decide on your reaction beforehand, when Ely attempt to bite too hard, a stern No, walk straight to the play stand with as little drama as possible, place him on his stand, turn your back and walk away. He will learn that this happens every single time he behaves badly. He will also learn that you will not hurt him no matter what. This takes time, it's hard to imagine such noisy birds appreciate a calm environment but they do. His grip on your arm tells me he is still nervous, a human perch is a questionable thing to trust when it's holding you up, he hasnt had a lot of human contact, he'll need time to process. He will learn to trust again and when he does he will want to do as you ask--most of the time. He'll still be a lovable mischievous Too. Music is a great distraction, most Toos love to dance, for some, a special treat is a good incentive. Eli has also had a very bad diet, if birds feel awful on the inside, they tend to get cranky. If the clip was extremely traumatic, that could be the reason for his aggression, he just isn't sure how these brand new humans will work out.
I should mention it's possible Ely has been traumatized by being toweled, if the sight of the towel scares him, find a piece of cloth that he can live with, your shirt, (yes, they will take the shirt off your back and laugh about it) a baby blanket, something he sees as a positive thing. Maybe a short perch, they are all individuals and have their personal hot buttons.
BTW, I thought your title in your other thread was very witty.