Jinny Has this daughter always ruled the roost like this demanding that everyone run their lives round her and her family? And is their a reason, why all of you, including her sisters have submitted to her demands and fulfilled them?
Was she ill as a child or did she have a traumatic eperience of some kind, so that everybody for good reason at the time ran their world around hers?
If this is so, then the time has come when it must stop. You must talk to your other daughters to tell them what you plan to do and ask them to also rethink how often they bow to their sisters demands.
The daughter in question has married, had children and formed a separate household so with her husband must decide on the best way to provide childcare for their children, without expecting her parents to be the solution to the childcare problem and any other they may have.
I am with all those who say, no argument, no discussion. Hand your notice in and get her sisters to do the same. If she turns up on the door mat the day after your notice expires, just refuse to open the door, and if she tries to use your grandchildren to emotionally blackmail you into continuing, just still quietly say 'No'