There's a really great book called Codependant No More by Melodie Beattie. I just finished reading it a couple months ago. It was really helpful to me.
I can really identify with all the things you've been through, as my life has been very similar, including losing my brother because of alcohol, although he was 16. My mother died from alcohol poisoning at the age of 49.
Al-Anon offers amazing support as well.
I'm codependent and an addict/alcoholic...in recovery for all three!!
It will get better!!