If your father has liver problems alcohol is the last thing he should be putting back every weekend.

It wouldn't hurt to suggest.. it seems you have a very open relationship with your parents.. take advantage of it.
Many of us will never be able to approach our parents as openly as you've been able to. If he says no, so what? his decision.. technically you can't make him stop drinking either.. but you can certainly try

Best of luck,
Just be honest and open with your parents... It's something that few of us are able to do.

Bob.