Just to add on to dogcom's comments about african greys, AGs are known to be a 1 owner bird, meaning the bird will only be bonded to 1 person and will appear agressive to strangers. AGs are also shy birds so even if they can talk and sing alot at the comfort of your house, that doesn't mean the bird will behave the same way out in front of other people.

These however, maybe overcame with frequent interaction of the bird with different ppl. But do note that each bird has their own charactor and personality, 1 method which will work with this grey may not be feasible on another.