Did you point out that you have wasted spent a lot more than 1 1/2 hours looking after your mother on his behalf as well as your own , and if he can't bring her halfway home on the Sunday, surely he could bring her halfway home on Saturday? And if he can't manage, can his wife drive her, either on the Saturday or on the Sunday, as originally planned? It sounds as though HE has to go somewhere on Sunday, not both of them. Do they have no shared responsibility?
What is his wife thinking of, saying that it is a "waste of time" driving an old lady of 87 home? Has she any idea how tiring 4 hours on a coach will be for her?