How do I approach my two siblings who have joint bank accounts with an elderly dad with dementia, but my name is missing in action?

I debated whether to include this question in the "financial planning" forum, and think it's best posted here, but feel this question about joint accounts is relevant to family relationships too.

My dad is 88, lives by himself but has around-the-clock aides to help him; he is a definite fall risk and recently had a minor stroke. My two sisters live in the same city; I live across the country. I am the reassuring daughter, whom he calls 2,3 or 4 times a day for comfort and to vent about his misery and pain. My sisters seem to have been spared of the phone calls to a larger degree - but this has been my life for over the last two decades since losing my mom. I am in town visiting him right now.

He was a smart businessman, but has not managed his finances well. You go into his apartment and there are stacks of papers everywhere. It is a big mess. A couple of days ago, I noticed that each of my sisters had their names on two sizable joint bank accounts, that together make up about half of his assets. My name is not indicated on any of the bank documents as joint holder.

A couple of years ago, I learned that they were listed as beneficiaries on multiple bank accounts but I was not.

I called their attention to it (as well as my Dad's). They took my dad to three out of the four banks in question, and got me listed as a beneficiary on most of the accounts where they were solely or jointly listed as beneficiaries. Unfortunately, he spread his money into so many separate accounts because of his paranoia with the economy crashing.

I truly thought the situation was resolved until I found out about the joint accounts. But being a beneficiary seems like a moot point on a bank account on which a sister is a joint holder. Doesn't the money become hers when my dad passes? Can she gift me the money? The will does state that everything should be divided equally.

It may just be a question of proximity because I live across the country. However, I have to ask myself what were my sisters thinking when they initially got their names on these accounts. I can't imagine going to the bank with my dad, as they did, for these important transactions and excluding my sisters. One of my sisters is a successful business owner and her husband is an attorney. That's the problem I am dealing with in trying to digest this.

I feel so resentful and don't know what to do. I have always been the sister who is "nice" and have too often given into my domineering siblings. These two sisters do not get along well, but I have had a good relationship with both.

They seem to be dismissive with me about the joint accounts when I asked. They don't seem to know much, and it's true that my Dad does not share financial information easily. Plus his dementia, paranoia about money doesn't make it easy for any of us. I actually found the statements in the mess of papers when I was looking for his long-term health care policy. I did call my Dad's attention to the beneficiary situation a couple of years back and he agreed begrudgingly to go to the bank. Now he cannot even leave his house, though maybe we could get a notary to come to his apartment if papers need to be signed for the bank.

I had a serious injury during a trip to help him relocate several years ago that has left me with a permanent disability. I am currently seeking employment but it is not easy when you're almost 60. My sisters are in much better financial shape than I am; I had to give up my college teaching career due to my disability.

How do I approach this without harming the relationship with my sisters, but avoid getting burnt after my dad passes?