How do I address financial issues for elderly parent?

As long as your dad is alive, you don't have 1/2 of the estate, your dad has the whole estate. He can do with his money anything he wants. I'm not even sure how they can separate out your half unless they change the documents to change how beneficiaries are paid out. If half the estate gets spent, then the remainder would still be paid out based on the percentages listed on the paperwork wouldn't it?

As for the family dynamics, unfortunately I don't think there are any easy answers there.

My take on it is this. Forget about what you expected to inherit and what the plan is now. None of the money or assets were or are yours in present time. It’s all your dads. If your father can no longer take care of himself and wants to stay at home, you are not obligated to help him remain at home. If your siblings want to give up their lives so your dad, who has already lived his life, can remain in his home, that does not obligate you to do the same. My suggestion would be have a family meeting discuss using dads money to pay for caregivers or place him in a facility.

You should do what you want. They have made their decision. They don’t get to decide for you. You should help when you want to help. Do it on your terms. You all have to think in terms of what is best for all of you. I personally don’t believe it’s in everyone’s best interest if it takes multiple family members have to take care of ONE elder.

You get your sister to stick to the original agreement by sticking to your original message "Sister dear, I cannot possibly help with dad on a regular basis. He has money to pay for help. I am not going to change my mind on our original agreement."

Your father clearly has assets and money to pay for in-home services and transportation. That your sibling chooses to be his primary caregiver is exactly that: a choice. Your sister's choices do not obligate you to change your choices.

If your father chooses to buy a house with your sister, that's his choice. It's his money and he can spend it how he chooses. And again, his choice does not obligate you to change yours.

Regardless of the inheritance, your father needs to spend his money on caring for himself. He also needs to put his important paperwork together including Durable Power of Attorney both medical and financial in case he becomes unable to make his own decisions either temporarily or permanently.

Your sister's expectations are unrealistic. I suspect it comes from a place of her feeling burned out from caregiving. Perhaps she did not recognize how much caregiving your father actually needs. But her solution - to buy a house and live with him - will not work unless your father pays for lots of in-home help. His needs are only going to increase.

I'm basically repeating Needto's answer to you. It's really very simple. No one INHERITS anything until after your father dies. You only inherit what is left after your father dies. If your father changed his will to leave it all to your sibling, then you have no inheritance. It ALL completely belongs to your father while he is living and should be spent to care for him.

Your father may be mentally intact now, and I certainly hope he remains that way, but you and your sibling have no crystal ball as to his future health or needs. You both may be blindsided by what he ends up needing and your sibling may find he/she can not continue to care for him and need assisted living or skilled nursing. I would suggest you all consult an elder care attorney and put the brakes on buying a new home with your father's assets. You could be seriously complicating things while agreeing to fund a new home for your sibling with your father's assets.

If your sister is waiting for an answer on your willingness to help I would tell her that a certified elder attorney well versed in Medicaid in your father’s state needs to be consulted in order to protect your father’s ability to utilize Medicaid when he needs it.
It sounds like sister is already burned out. Many a caretaker has good intentions until they realize they just aren’t able to provide the care on their own and that the price of care will exceed the elders savings.
Obviously if he needs care then it must be paid for and ALL of his money will need to be earmarked for that care and the portion spent needs to be well documented.
There is no need to be angry.
Your position on saying dad should pay for his own care is correct. I would stick with that. If she’s already made a mess of his finances, then the lawyer is even more important.

So your dad is mentally intact and social and your sibling is already angry and upset that you are not available for care, what kind of care does your dad need?

Does your dad live with your sibling yet? This will only get worse down the road when they do live together if they aren't already.

If possible try to stop your sibling from using dad's proceeds from HIS home to purchase another home for the sibling to share. Your initial decision, that proceeds should go for his care in assisted living was the correct one imo. In fact I think you should talk to your father about this and encourage assisted living.

Seems your agreement was more than generous. Also seems your sibling is getting burnt out doing all the caregiving. Reinforce that your "share" of the estate was to provide for care of your father. Suggest that sibling hire somebody from a home heath care agency to care for father on a regular basis to give sibling "breaks". If this is not suitable, maybe it is time to use inheritance to place dad in assisted living.

I would absolutely refuse to be made a hands on caregiver. Talk about taking an inch a mile! Sheesh!

I would make it very clear that dad can do whatever he wants and so can your sibling, as long as it doesn't include sucking you into their plans.

How convenient for your sibling to get everything dad has left in writing and then run off leaving you to deal with him.

I would be very clear that you WILL NOT be participating in this bad idea and that you are willing to go no contact if you are pushed and prodded in any attempt to manipulate you.

Can you have a private meeting with dad and encourage him to find and move into a retirement community? If he doesn't need much help and he is social, this would be a great way for him to have a life and let his adult children have their own lives. Hire an aid for the things he needs and let him do his thing with his peers in the community.

Make your mantras with your sibling "I can not possibly do that!" and "Not happening!"

Best of luck standing your ground no matter where they go to manipulate you. You are not obligated to support their bad choices.

Your husband is 100% spot on. He is obviously willing to support you, use it. If need be he can tell sibling to leave you be, there is an agreement and that is that.

If the sibling plans to provide 24/7 care to your father for the rest of his life, then it might make sense for the sibling to buy a house, with a mortgage that the sibling would be responsible for.
But the sibling should be aware that care giving needs expand as the elder ages. And the sibling may end up needing outside help, or the father may need AL or a nursing home. Then the father's wealth is tied up in a piece of real estate that provides no liquidity for care. Sibling should be aware of the potential downside of the proposed arrangement before proceeding.
And you should reinforce that you cannot be available for hands on care in the future if things change or extra funds if they are needed for AL/nursing home.

Several hours away makes it hard to be hands on regularly. Plus holding down a job. Maybe occasionally give her a break by spending a week so she can go away.
But, you have agreed to give up your inheritance so she could get help. Did they need another house? I think you have done enough. Its not even logical to think that living as far away as you do, that you can help out.