From the sequel: Celia and Megsie have to work together to prevent Isabel from signing the farm over to the uncle without letting on that the Disappeared Dad may be alive before proof is in hand. It's not the Bavarian Fire Drill that follows (with Celia going Eek, a Mouse!! like crazy), it's Celia trying to instruct the Megsie's next move while still screaming.
The following exchange in the first movie, between Selma Quickly and her friend.
Mrs. Quickly: "...What do you take me for, some common-" *cut off as she hears a knock at the door*
I know what he wanted, and it wasn't marriage! No wonder there are so many of you.
The children manage to keep their Great Aunt Adelaide from taking one of them by passing off the scullery maid, Evangeline, as one of their siblings, so she could be raised and given an education and the actual siblings wouldn't be broken up. At the end of the movie, Mr. Brown and Evangeline finally admit their love for each other and agree to marry. In the midst of the congratulations, Great Aunt Adelaide gives a horrified cry of "Incest!" This then leads to Mr. Brown having to explain to the priest that no, Evangeline is not actually his daughter.
After continually startling Mr Brown by appearing behind him from out of nowhere ("I did knock") Nanny Mc Phee then appears in the kitchen while Ms Blatherwick is cooking. The cook turns to spot her...and instead of being startled, casually gets on with what she was doing.