I have bought 2 cockatiel birds around 10 months ago, one lutino and one cappuccino. I'm not sure of their age at the time I bought them. I bought them from a pet shop and they were in very bad condition there.
My lutino cockateil is very violent sometimes and I'm not able to understand how to handle him. Every now and then he runs after my other cockatiel and bite him. Also every night he fights with other tiel inside the cage. Also, I've noticed that as I tries to put cloth on his cage it shows it displeasure by gesturing bit on cage and cloth.

When I bought him he used to bite a lot to me and my other tiel and certain time I hit him in the past for that behavior. I now realised that my hit made him feel threatened by me and I'm not sure how should I overcome this. I tried stick training. he comes eat and still behave similar. I'm getting really frustrated and not sure if he will ever trust me. I'm wondering would it be good for him if he has new parent. I don't to give me away, but I don't know how to keep him happy. I really want him to feel safe and loved but he is really afraid of me and very violent on my other tiel

Please help me.