Denial may come into play here too. You react to Dad's drinking binges by smoking marijuana to calm down. Parent may see no problem in new partner caring for children despite an alcohol problem. Having too flexible boundaries means you bring in new problems. GParent may believe Parent has relapsed but hide this from agency.
Rigid boundaries hide problems.
Parent may believe it is ok for GParent to raise Child, especially if GParent did not raise Parent. Parent may feel GParent can not raise children well, but may hide this from worker and agency to avoid losing Child. The difference is that the Alcoholic Family is participating in the alcoholism and needs treatment, while the Family with an Alcoholic can exclude the abusing member and avoid or limit further trauma to the family. Therapy may also have to address couples work. The 12 Step model includes that partners should not go to groups together, as it should be Anonymous and individual because the problem is only solved on an individual and even day by day basis.