If elderly parent has joint account only with one child, will other children be disinherited from those accounts?

All I know is I honored my mother's wishes and the terms of her will. Whether they were probatable or not. She wanted her family whole in her passing and I made d*mn sure it happened.

I tried to get sis on mom's account, but she could not make the time to go to the bank and provide her signature. I watch out for bills, taxes, legal stuff and simple medical. Mom is still independent, but bored so sis invites her over on weekends. There is a will, but, with one or not, I would never think to do anything other than what they wished. Pay bills, sell remaining assets, split profits, and like Jeanie, by the time all is said and done, we may be toasting at MacDonalds.