Um...you said the bird belonged to your mom before you had it. Did your mom live somewhere else??

Your bird sounds VERY unhappy. I would imagine that with all the things that happened at your house, he would be VERY scared. I feel very sorry for him.

He CAN sense any frustration or any negative feelings you have...even when you aren't in the same room. Have you done your research on his breed?

Have you talked to your vet about this?

EDIT: I need to add something. You said your bird hisses. We've had cockatiels my entire life and I've NEVER heard them hiss, ever. That really concerns me your bird is constantly scared.