My father drank like this. He might have drunk slightly more in terms of units, but pattern was similar: no spirits, beer then wine, so it "sounded" sort of like normal social drinking in the evening and not an alcoholic sneaking swigs of vodka under the table at work.
The fact is that it is still alcoholism. And if he's having closer to a bottle of wine a night and four pints of strong lager then it's more than 100 units a week. The question is how to get him to see the damage it's doing to you, his DS, and his health. My father said (when he was dying of cirrhosis in hospital) that he just hadn't basically realised that drinking at this level could kill him, and as a younger man (30s/40s) felt invincible.
I truly think the only thing that would have got him to stop was seeing the state he would end up in (for many years before he eventually died he was in bad health and in and out of hospital with cellulitis, various blood infections, struggled with walking, vomiting, unable to eat normally etc). I don't know how you achieve this but I think seeing someone with end stage liver disease and having a sensible doctor talk frankly about the risks would be really useful for him. It's a very pernicious disease and sufferers are selfish and sneaky. If he doesn't want to stop for himself he won't.
Does he smoke? My only other advice would be NOT to put pressure on him to give this up at same time or maybe even to cut down. My father was a pretty light smoker but under pressure from GP and others eventually gave up with extreme difficulty. At that point he actually started drinking more because didn't have punctuation breaks of smoking / other thing to do, and was diagnosed with liver disease within a year. (Could be coincidence but I don't think was.)
My other suggestion would be to give him more responsibly so he HAS to change his patterns -- e.g. could you increase your work hours slightly so he has to be responsible for DS one night a week? In a weird way I think it gave my father a lot of confidence when he realised he could get through a single night without alcohol: before he seemed to think he would explode or something.
And are there underlying sleep problems? (There will be sleep problems from all that drinking, but maybe he's scared of insomnia without knocking himself out?)