Have tried every angle short of direct force. How do you get a proud, stubborn elder to admit help with basic tasks is needed?

As the others have said, it's not your job.

Also, for the level of activity he's doing, one meal a day might be plenty. My mother lived on nothing but Ensure for the last seven months of her life, so it's entirely possible to do.

My mom fought showers like nobody's business, and it turned out she couldn't stand having water on her face and head. She thought she was drowning. (She couldn't swim and she had dementia, so the two got tangled up in her mind.)

I finally hired a caregiver to give her showers, and Mom was grumpy but acquiesced. I'd call it her "company manners" when she'd give me or Dad a hard time but not pull that stuff with a stranger. That might work with Dad, too. You're safe to fight with because you'll always be around no matter what and won't leave him. A caregiver might go out and tell people he's an old poop.

It's all fine and dandy that everyone wants Dad around for years to come, but he does have some autonomy and maybe HE doesn't want to be around. Be respectful of him and his decisions. He's an alcoholic and elderly, plus he has dementia/Alzheimer's. He's not going to get better.

You don't.    He isn't going to change; you have to find another way to support him in the services he needs.   

And you reassess the "it's my job" approach.  

This sounds a bit caustic and blunt even though that's not what I'm saying.  I'm just acknowledging that some things and some people don't change, and frustration only will be the result with someone who's uncompromising.

There's also the addiction issue, and that could be a major insight into this man's personality and willingness to change for his own good.

Your FIL is his children's responsibility. As said, if he has a Dementia, he has lost the ability to reason. You cannot force him to do anything. His short-term is probably gone or going. He processes what is said to him much slower. And being an alcoholic doesn't help.

What do you do for him? You may just need to step back. My daughter, RN, worked in SNFs for 20 years. She says you need to make the person feel like they made the decision. Like with a shower "Dad would probably feel much better if you had a nice shower and clean clothes. If you get one, we'll go out for a ride" They have made the decision.

Your FIL will only get worse. Something will happen to land him in the hospital. Thats when you get him evaluated and diagnosed with a Dementia. His children then will need to get onboard. None of you need to take him into your home, but you will need to find him a safe place.

Don’t be his caregiver in any way, this isn’t on you. He’s not going to change, except to worsen. I hope your husband or another direct relative has POA for his medical and financial decisions for when the crisis time comes, and there will be one. But meanwhile, back off. He may never see his need for help, but most certainly won’t see it with you and others trying to fix everything

"...hiring outside the family is a no go, "thats my job"...

So, you are being "assumed" into being his caregiver? For an active alcoholic? If I'm understanding your situation, that's a hard no on every level. Anything that anyone attempts to do for him will be cancelled out by his drinking. His family (including your husband) sounds like co-dependent enablers. Don't get sucked into it, it is dysfunctional. The consequence of his drinking is no one provides for his care (until he dries up). The consequence to his enabling family is that you're not the lackey being sent on a pointless mission so that they can feel better about themselves. Hard NO.

If someone is his DPoA then they can manage his financial and medical affairs but he still won't cooperate, so why bother?

If none of his children are PoA for him right now, there's nothing they can legally do to force any care on him anyway. Their choices are: call APS on him when his living conditions get bad enough. Eventually they will pursue guardianship and move him to a facility and manage his affairs. Or, his children pursue guardianship themselves and then still have to orbit around an uncooperative drunk. They can't force their dad do help himself so they're trying to force you (it seems from your post info). I wouldn't get involved if I were you. Just say no.

You say that he has Alzheimer's / dementia.
If that is the case then with some of these things he does not have an option. He can not make rational decisions any longer.
You can get someone in that will probably be able to get him to get into the shower easier than you can.
You can offer a meal but if he refuses to eat that is his choice.
I think your husband should be the one to do much of the caregiving since this is his dad. And it is possible that your husband might be able to get his dad to do things you can't.
In your profile you say he is living at home.
I do hope you mean he lives with you and your husband, or that you and your husband are living with him. If your FIL has dementia he should not be living alone.
You might want to consider Hospice. With Hospice you will get a CNA that will come a few times a week to bathe/shower him, You will get supplies ordered and delivered. A Nurse will check on him once a week, more often if needed. And medications will be delivered.

Have you thought of working harder on accepting his choice?

Step back. If every strategy in the world won't change his mind, what is the good - the purpose, the benefit to anybody - of continuing the attempts? Leave him be, and hope that eventually he will come to you.

And frankly, it isn't your responsibility either to spell out the consequences of his choices. To avoid future temptations to say "I told you so" you could raise this question with your husband: is he sure that his father has given it enough thought, and if not how might he (your husband) talk to his dad about the information he needs to be aware of.

But don't cross the boundary. Not your Dad, not your choices, not your responsibility, simply not your problem to solve.