Sorry to hear about your father

I think you know already what he needs to do.

The alcohol must stop. That will put huge strain on the liver.

Stress is definitely always a problem and can cause many un diagnosed problems. Sadly in his case the bills are his driving force.
If there is any way to down scale your debt requirements that will allow him to work maybe a day a week less.

Sleep is very important. 8-9 per night.

And yes diet. For you are what you eat. Fresh fruit, an abundance of fresh veggies, some meat (grass fed/antibiotic free) at best.

Juicing veggies/greens is magical to the body. (as already mentioned various time before my post)

Drink plenty of water. Tap water is poisoned so seeks clean un fluoridated un chlorinated source.

All of these tips can be introduced slowly. A step in the right direction gets you closer to your dads health.