In that Always Brisbane 2013 he seemed upset or something when singing..
Why does your father think his voice was damaged in 2013?
Just wondering. Just saying his voice was damaged ain't enough for me.
Emotions can cause you to forget, overuse, etc. He used way too much twang in Brisbane, etc.

When I become emotional (For example when someone dies or so) my voice becomes a bit raspier and it feels like an effort physically to talk (Have to push my voice) and sometimes my pronunciation becomes worse and I even sometimes say words in the incorrect order.

Vocal damage doesn't really sound like that.
Vocal damage or irritation is often cracking, raspiness, croaky, breathiness, loss of range, etc.