Welcome
I don't know much about how to help aggression in parrots, but like wolf says, you will need a lot of patience, consistency and persistence.
if hes not already, introduce him to fruit and veg - a good healthy diet helps with aggressive birds.
Also, he needs plenty of stimulation, foraging toys is a must, it will keep him busy and keep away the boardem.
He needs to learn that he is safe with you, association is the best way to do this.
The cage you have, is it his old one? If yes, hes been tethered to it all his life, and is very territorial over it - its been his only safe place. But also, it comes with a lot of negative memories, which he'll still associate with. When he begins to get comfortable with you and your husband, you might like to get a different cage.
A good place to start positive reinforcement is getting him thinking "hands = treats = good thing". When hes not biting or being aggressive, offer a treat. At first you can place it in an open palm, far enough away from him so that he doesn't feel threatened, once hes interested, you can then place it down and walk away, if he is in his cage when you do this, put the treat as close to the door as you can, so your hands don't invade his space too much. Over the weeks, he will recognize that your hands are the ones giving him good things, you can get closer and closer, and soon he will trust your hands enough to take the treat from them

then you'll be able to work on the stepping up command with him.
Good luck - and thank you for giving a parrot a second chance at life, your an awesome person
-> my boy wanted in on the conversation -- #4bn vhgfft