Boketh

So my wife has a congo african grey that is 25 years old (she is also 25) she has lived with him her whole life but the only person the bird let touch him was her grandma and ever since she died nobody else has handled him or really showed him any attention. For about the last 8 months i have been trying to get Casper to let me pet him or step up onto my finger, I feed him peanuts and almonds through the cage by hand every day multiple times a day and every now and then i can touch his head and give it a quick scratch. Every time we let him out of the cage he always comes right over to me when i sit on the ground and then he bites the hell out of me lol drawing blood everytime on my fingers, hands, arms anytime i try to get close to him he bites me hard and then i yell at him so I guess he thinks its a game now lol. I love the bird he mimics me and my wife and our kid all the time and I wish that I could get him to step up on my finger or even just let me pet him without getting my fingers ripped apart. What can i do to build more trust and to get this guy to stop biting me and to actually be apart of our family without everybody being so scared of him?