Welcome to the SR family!
I'm sorry that your son has found another soft landing. And it happens to be a single mom with her own child to care for. Ugh!
Have you tried Alanon meetings for yourself? Your daughter would also benefit from the support at Alanon. The meetings are based on the same 12 steps of AA but tailored for friends and family members of alcoholics.
Please make yourself at home by reading and posting as much as needed. Here is a link that contains steps that have helped some of us:
http://www.soberrecovery.com/forums/...l-problem.html