6oz every 3 hours is fine, babies don't like following their siblings unfortunately.
I stopped the night feeds by pushing them back slowly. So at first I'd not feed before 3am, then 4, then 5 then 6. Occasionally she'll need it and if she's really going mad, I'll give her 3 or 4 oz, as it might be a growth spurt but otherwise it's fine. It happens like once or twice a month at the absolute most.
What times does he eat food and nap during the day? Sometimes eating lots of very fibrous foods like avocado and banana at dinner time can mean they are too full to drink enough milk.
Can you try pushing his nap a bit later so 1 to 3 instead of 12 to 2 for example, and then he might go later. It seems he is in an ok routine sleeping 11hrs, but you just want a later wake up time.
I know some people offer water at night instead of milk to see if they are thirsty or just trying their luck with milk but I've not done that personally, only because I didn't need too.
We also use a dummy so I think that l might help us! Not sure if you do