Frustrating I know but it wasn't your words or feedback that 'shut him down'. It won't make that much of a difference to him until he is ready to seek recovery on his own.
The interesting part in your story is that I read somewhere where (outside of AA) neutral third party professionals (like a cop, nurse or judge) seem to be able to get messages across to the alcoholic about the damage they are doing to themselves.
Probably because they don't have the emotional investment so the alcoholic doesn't go on the defense. Who knows, maybe some of what the in-law said sunk in.
Regardless, it is what he does with any information that matters. If he isn't ready to commit to stopping then I'd not waste my time researching or educating no matter how valid the info is that you want to share.