Siblings upset with me after I walked away from my nasty father. Having mixed emotions over this - guilt is one.

No one who was abused by someone should be expected to care for them in the senior years. No one.
That your sister did not experience what you did does not entitle her to expect your assistance in his care.
If you have a good relationship with your sister, you can tell her you're willing to help HER with things she might need, as long as you don't have to be in contact with your dad. If she can't understand your feelings, there's not much more that you can do, other than to try and keep the lines of communication open with her.
Your mental health matters, and trying to bury the feelings about your dad will cause you nothing but pain. I hope you can reach a resolution with your sister that will work for both of you.

Tell your sister to practice what she is preaching.

She wants you to forgive and forget abuse, yet she won't accept that you can not continue to be abused by this man, so she isn't forgiving you for her having to take care of him. Maybe she is more like him than you know.

You are correct in keeping yourself away from the abuser, regardless of what he is to you.

My sister has NOT been apart of my mothers life for years ..more than 20yrs. She is 7 years older than me and has her own past with my mother that i am not aware of. (some things I am aware of) I wish my sister well. She has no idea what my mom is going through (dementia) and my sister has isolated herself apart from our small "family". I am here taking care of our mother by choice.
I am sorry you were abused by your father. No-one deserves the wrath of someone else's wounds and sickness. Your little sisters experience is much different and its okay for her to have a relationship with her father. Your experience is very different and its okay for you NOT to have a relationship with your father.

Whenever people use the G word (guilt) I ask them to search for another word. Semantics matter. Unless you are a felon you have nothing to feel guilty about. You may well feel DISAPPOINTED that your siblings don't understand that you are done with abuse and have decided not to risk it entering your life again. You may be unhappy that you are not a selfless Saint seeking martyrdom and the word "thanks" which of course you won't ever hear from this family. You might feel worried that your father, always abusive is now ill and hurt that there will not be any redemption. You might feel confused about what you are able to do and still keep your sanity, and what you will CHOOSE to do in future. But after years of abuse I doubt that "guilt" is what you really feel. When siblings grow up in an abusive household they often become either abusers or recipients of abuse habitually in adulthood. You have done the right thing, broken the chain and walked away. Whether because he chose to or because he was inadequate at parenting, your Dad was lost to you long ago. The siblings made their own choice. You have offered what you can. If there is more you would LIKE to offer, do so. If not, continue on. If your siblings are angry and abusive, walk away from them as well.

You are responsible with your siblings to see that your dad is safe and cared for. You are not required to have a relationship with him.

It seems to me you're doing what is required and no guilt is necessary.

I'm really sorry to hear that you've had such abuse from your father and that you feel isolated from some of your family. I understand your feelings of guilt - this is quite a natural reaction if you are a caring person but are unable to help your father in this situation. Your past history with him and his violent, abusive behaviour really gives you every right to be cautious and wary of being in contact with him again, despite his illness. You distanced yourself from this in the past for very good reasons. Getting directly involved again now could lead to further abuse. It is very good of you to offer financial assistance, which is a lot more than most would do after such bad treatment. If your sisters and other siblings don't want to accept your financial offer, that is up to them, but at least you have made it. Don't be pressured into doing any more than you are comfortable with. It might help you to write a letter to him explaining why you cannot do any more and that you wish him well. You don't even have to send him this letter, but it would allow you to work through your feelings and help you to explain this to others. Please put your own wellbeing first. After my own father died last year, I had to walk away from my abusive stepmother as her cruelty towards me around the time of my father's death put me in therapy. I'm not happy that I've left a widow on her own, and said goodbye to a relationship of over 30 years, even though the abuse was always there. I feel guilt about this, but my therapist has helped me to see that I must put my health first and that other people are responsible for their own actions and have to live with the consequences. I hope this helps you to stay strong.

You have no obligation to care for your abuser. You have been made to feel inadequate all your life so that’s why you feel guilt. Find some counseling to help you heal from the abuse. Are you close with your siblings? Doesn’t sound that way. So you will be scapegoated anyway - no matter what you do. Stepping into a caregiver role would be suicide. Be thankful your younger siblings were spared, and explain that to them if you want to. Otherwise you don’t owe anyone an explanation. It’s hard to not have your truth validated. I know, I’ve been there. Be direct with your siblings: “Dad beat most of us; he was physically and emotionally abusive to me and it’s not a good plan for me to be involved in his care. I’m happy you were spared. So you need another plan.” Wishing you comfort and peace.

You don’t need to forgive or forget. Mental illness is no excuse. If your dad wants your forgiveness then he should ask for it. Your sister has no right to tell you that you should forgive and forget.

You didn’t dump all the caregiving on your siblings. If they chose to do it, that’s on them. You had every right to walk away. And I’d say your dad did the dumping by failing to plan for old age. You’ve done more than a lot of siblings have done by offering financial support. I agree, your sister needs to practice what she preaches and forgive & forget!

are you totally cut off from all the siblings? What is stopping you from reaching out to them? Your youngest sister, it seems she thinks she’s calling the shots? Don’t let her drive a wedge between everyone.

You have my total understanding. I was the only surving daughter, middle child of 7. In the process of protecting myself from mother, emotionally, I never really knew her. After high school, I moved hours away to attend school and avoid contact with her. When she finally apologized for her neglect and emotional abuse, (night of her mother's death), it was too late for us. I contributed as I could, provided a home when hers was irreparable from neglect, with no assist from siblings. In her last days, I was the only one with her up to her last breath, "they couldn't handle it." The resentment turned to regret for the relationship we never had. My brothers were still young when I left, and likewise prefer to remember otherwise. I did what I did for my father, with whom I shared adoration and respect. I thought, if that wonderful man loved her, must be some good somewhere. Your tragic situation involves both physical and emotional abuse. That's tough to ignore even when his days are numbered. I suggest having someone other than family ask if he'd like to see you, and if so visit briefly without siblings, keeping conversation on level of your comfort zone. Its all going to depend on how important peace with your siblings is to you. Forget about changing their mindset, they can't relate. Like you, I have no pleasant memories of my life with her. What I did was based on respect of her position as my mother, certainly not her performance. One visit should suffice. Again, keep it private with understanding that he may say something thoughtless or even apologetic. Don't feign affection you don't feel and he didn't earn. You could not have escaped that era without great personal strength and self respect. Let it guide you and you will do the right thing. Be kind to yourself.

No one should have to care for anyone that abused them Physically or mentally.
You can support your sister. If she wants it and if you want to give the support.
You can help her or her family while she is helping your father.
You do not have to explain, you do not have to rehash what he did just tell her that you can not care for him personally.
If she or anyone else in the family "doesn't get it" there is no need to explain your decision.
Do not let the feeling of guilt make you do something that will be harmful to your mental health.