Welcome to the Board, Katy. You've come to the right place, and a
good place.
And with that:
The truth is there's very little you can do in terms of help. The only way an addict or an alcoholic will quit what they're doing to themselves is if and when they decide they've had enough and follow that decision with a course of treatment. And then it's a lifetime of self monitoring for them from that point forward.
Hopefully, your cousin is aware of Al Anon and Nar Anon, which are truly wonderful programs and help the loved ones of addicts and alcoholics regain their lives and their sanity. There is also the "Friends and Families of Alcoholics" side of SR that she can join if she's so inclined.
Dealing with a sick spouse is one thing. Dealing with that AND a sick child is pretty rough. My hope is your cousin checks out Al Anon/Nar Anon, but she's going to have to make that call on her own. You can't make that call for her.
If you want to learn about what it is you're up against, a good starting point is a sticky note called "What Addicts Do". It is a blunt, stark statement of fact written by an addict about addicts, and it is located on our homepage. Read that, then read it again, and then again...and keep reading it until it sinks in. Because that's exactly what you're up against. Addiction and alcoholism are mutherf**kers to deal with. They destroy lives every day across this country and across this world. But remember this: your cousin should not pay the price for the decisions of her husband or her son.
Again, Welcome to the Board.