Time and very slow. I have a son 26 and daughter 24 that are at extreme risk, their mothers side is littered with alcoholics and on my dad's side three dead to alcohol, yes I was always told I could never drink but I never listened (no one in my family of five including my parents have ever drank, only me the youngest). I have had this conversation many times with addictions counselors trying to come up with what/when/how to say something, just subtle remarks is about all I have been told.
In a way I don't understand in my daughters case as she is in her final year of research then she will have her Dr. degree in genetics so I would think she would understand of all people but for now they reject any mention of it, so I wait.