I think my dad is an alcoholic
Why do you think your dad is an alcoholic?
Because every night he drinks and abuses my mom, and it makes me cry with fear and sadness.
I am sorry that you are going through your situation.  You should get counseling for yourself and try to find a way to get your parents help as well.  If your father is struggling with alcohol, he needs help before it does permanent damage to him.
My father's drinking problem has not reached the level of needing counseling, but it is starting to make me angry.
I can understand how it's making you angry, and if it continues even after you speak with your family about it you might need to seek help because it will just get worse.  No one should be getting abused by an alcoholic regardless of the situation, so you should be proactive in helping your mom and dad.