I would definitely believe that they were 'entitled' to more of the inheritance. If it were me care-giving, I would probably not expect any more inheritance, but it would be nice for some extra $$ from a sibling while the parent is still alive for expenses.
I recently found out some old (really old) family gossip that I found fascinating! My grandmother had 3 siblings, 2 sisters and a brother. When all the kids except the eldest got married, the eldest stayed in the family home, had a small job but not enough to live on, and she had no time because she was caring for her parents.
Her parents eventually died. My grandmother & other married sister wanted the brother to pool each give their shares of the house to the sister who was basically a spinster because she was the caregiver. She didn't have enough of a job to support herself and had no where to live except the family home. The brother, however, said, "tough" and wanted to sell the house, divide the $ up 4 ways and, to heck with the other sister.
My grandmother and her married sister decided to pony up the brother's portion of the $$ he would have gotten from the house (this was during the Depression!) and they did, so the older sister could stay in the house. They had no hard feelings, all three sisters were very very close after all this happened. However, the brother - whom I'm never met even though he's my great uncle - was never spoken to again. I'd never met him, and his name was never spoken ever again.
Sad, but I so rally around those women that were behind their sister that they somehow found the money to buy the brother out so they could take care of their sister. Good riddance, Uncle George!
What a great story! And very familiar to me--but it was my mother and her sisters/brothers with my grandmother's estate. A little bickering went on but eventually they all agreed to let the one spinster sister keep the house--no one had pony up any extra money for a rebellious sibling.