Hello
today I have a question concerning my Galah. For the past few months he has been aggressive towards myself and everyone else that he comes intact with, what I mean by that is he's friendly with me sometimes but cant be around anyone else. He was once friendly to whoever he meets but after an incident with my mother he has been aggressive. The incident was when i was in my room with him and she came and and he flew towards her and my mother who freaked out hit him, (luckily there were no injuries and I explained to her that she cant do that afterwards). But now i cant do anything while he's out, such as get up from my seat, get a change of clothes, put something away, move from one side of the room, unless i do it very slowly. An example was today, we just got a new pair of budgies that aren't tamed yet, so i brought him out to introduce them (the budgies were still in their cage) which I've done before previously and he went up my arm and bite my cheek, leading to him attacking me. When he usually attacks me I crouch down and curl up in a ball since when he attacks he does it a few times. Is there a way that i can reduce this to where he can be a friendly bird again and gain his trust again? please I need help. Ive also have been able do do some training with him, and I'm able to bathe him as well.
Note: he's also a rescue whos been through 4 homes.

Note: he's also a rescue whos been through 4 homes.