Worried about brother's drinking

We've felt that my brother (48) drinks too much for maybe 5+ years now. My sister in law hit a wall with trying to talk to him about some time ago.

I've only really had one chat with him about and he shut down pretty quickly. I told him I was worried he drank too much, and particularly in light of the likely link between alcohol and Alzheimer's Disease; which is what our dad has and we are his carers. I was conscious not to push it and really that was about all I said before we moved on.

I have moved in with my dad to look after him full time. My brother comes over once a week. We had already agreed that dad couldn't handle alcohol anymore and we got a stock of alcohol-free beer and wine so that he could still enjoy a glass over dinner without any of the after-effects.

I went away for 3 days to a wedding and my brother covered me and stayed with dad. The recycling bins were collected on Thursday morning. By the time I returned today, Saturday lunchtime, there were 3 wine bottles and 8 beer bottles in them.

I'm furious, frankly. That's a lot for 2 days and an evening, right?

I don't know if he has been drinking it alone or with my dad. Either way it's bad. If he's drunk it all by himself then he's drunk on the job of looking after our dad, plus the harm he's doing to himself. If he's shared it with dad (none of the alcohol-free stuff has been drunk) then he's prioritised his own need to drink over our dad's health. He already told me that dad had been very confused and upset in the mornings and couldn't get up until midday so now I'm left wondering if that's because he's suddenly got alcohol in his system again.

It's been my first break from full-time caring for months and I had such a great time catching up with my friends. But how can I do it again if I can't trust my brother with alcohol?

I know I have to talk to him about it but I don't know how to broach this...