I'd like to see a book covering the re-integration of the Bettany family. The parents haven't seen the older set since they were age four and under, the older kids have likely been fantasizing about having their parents back for years, while Maeve and Maurice are used to being the only kids in the family and are suddenly the youngest, with the other four siblings all knowing each other well.
There are brief mentions of Maeve resenting Peggy trying to mother her and manage her, and also of Maeve and Maurice resenting being apart when they were sent off to boarding school separately.
I think that would work really well as one of EBD's holiday stories. She was still at the height of her writing prowess round about when it was set and Exile, Rescue, Monica and Three Go were of that period and all have at least large chunks of non-school based story.