First and foremost is understand for yourself that you may not be able to change what is happening in real time but can begin to plant the seeds that will foster change later.

Lead with being a good listener. What I have found in my experience talking with many individuals struggling with this is that they have grievances, they have a sense of not being heard, therefore not understood, therefore not ever validated in their own experiences.

Listening can lead to a sense of being heard which will strike them as different. Enough to perhaps stay involved in the convo or to at least think about it later.

Lead with empathic responses and approaches.

Try not to rebuttal.

Try to remain calm no matter what you are hearing.

Avoid being or sounding judgmental.

Remind them you love them unconditionally, even if you cannot support their actions, lifestyle.

Remember listening is not a sign of conceding or agreeing, but rather an indication of the worth and value you have concerning that person.

Avoid "cutting the person completely off". You can still maintain healthy boundaries and limits. There can still be accountability but think of how to apply that compassionately.