I really feel for what you are going through right now. There are three children in my family - I'm the middle child - the "emotional one" as my Mom would say.
My brother (youngest) and I took care of Mom during her cancer treatments and then the last month of her life. We were told 3-4 months but it turned out to be just 18 days!
Both my brother and I had promised Mom in our early 30's that we would be there for her. Her worse fear was being put in a nursing home and we assured her that "it will never happen". We were very proud of ourselves when in our mid to late 40's - we were both there for Mom - we kept our promise! We would compare phone conversations we had with Mom and finally discovered that she was trying to "snowball us" by saying one thing but something totally different to the other. That was when my brother and I realized it was time to get to Mom NOW! My brother would "dance" Mom to wherever she needed to go - he was there for strength, I was there for her dignity. Mom was fully capable of getting up and about but later was weak and dizzy. My brother made sure she would "look at me" when standing her up - that stopped the dizziness.
Mom never lost her sense of humor all the way through the end. All three of us had "situations" and talks that would make us laugh - sometimes my brother or me would hit the floor laughing so hard with tears flowing. Mom couldn't laugh as hard as she used to do - but she kept a smile on her face (even though it got weaker and weaker)!
The oldest sibling "could not be bothered", it "didn't fit in her social calendar", her "babies" (youngest was 15) were sick. It became a "you answer the phone - no you answer it" between my brother and I - if it was the oldest sibling - I just hung up the phone. Oh, and my favorite - when my brother called to tell her "Mom is terminal", her response - "just call me when she gets worse"!!! What is worse than "terminal"?
When our Dad had cancer - the oldest didn't want him to have any treatments - which Mom told her then where to "get off"! She didn't want Dad to have a full military honored funeral - Mom let her have it! She was told to "ride back of the line of cars" when it was time for Dad's funeral. She used an "humanitarian move" with the military to live in the same city as Mom and Dad but not once visited Dad or Mom. Her children (4) were not allowed to see their either one of their Grandparents one more time nor did any of them attend the services.
When she decided (after my Mom asked my brother to call her daily and he would do it there with Mom) she was finally coming to see Mom but she would be by herself - after my brother hung up the phone, Mom stated "I don't even want to see her". Angels came and got our Mother that night.
When the oldest arrived at the house and started yelling at my brother for "not picking her up at the airport and that he owed the cab fare and what do you have to say for yourself" - my brother told her "we were a little busy this morning, Mom passed away and they have just left with Mom - pay your own cab fare" and he closed (not locked) the front door. We both went out back to Mom's patio while the eldest had to bring her own luggage in (I'm sure she isn't accustomed to doing something so "demeaning"). She came out to the patio, I got up and went inside - after all I "ruined her cruise" when Mom had informed her of my 17 year old son's death in an auto accident 6 months before Dad passed! And at Dad's funeral, she had the nerve to tell me to "get my daughter out of the room (where our Dad was before the services) so she could have some time with "her father"". I looked at her and told her, "my daughter will leave when she is good and ready - at least she visited him in the hospital - you will just have to hope there will be some time because after my daughter is my turn, then our brother's turn so I doubt you will get a chance".
All three of us lived out of state during Mom's battle with cancer. It didn't matter to me and my brother - a promise is a promise. When were brought up with the "Golden Rule" - the eldest sibling "never got it".
Twenty months after losing Mom, I unexpectedly and shockingly lost my beloved brother. I truly feel like the "sole survivor of my childhood family". There is no reason to want to even talk with the eldest sibling - she sued my brother (Mom's Executor) because she didn't like what Mom did with her assets! Then she added me to the lawsuit when notified by the Court of a hearing date change because he was having surgery for bladder cancer! What a "loving family member"! As far as my brother and me - she no longer was "family" when she couldn't come see Mom or be "bothered".
I don't think an outsider could have helped us three! At the funeral home when I finally got to read the obit the oldest had composed, it had a grammical error. I said something about it - my brother did the cat "hiss" and told the funeral director that she would have to solve it. When she told the oldest that I was right - her reply, "well it depends on what you think". When asked about the flowers, her response - "we don't do flowers" - my brother promptly dismissed her from the room.
After all our folks did in raising us to be caring individuals with the "Golden Rule" and "when you make a promise - you keep it" - the oldest sibling "never got and never will"!
Sending hugs and hoping maybe another insight to someone else's dealing with siblings that "know it all" but "don't have the time" might help. You do as your "gut" tells you and you do it with love! You will never regret it!