The Bagthorpe Saga comprises ten books (though the tenth is terribly hard to find), beginning with this one, Ordinary Jack. They are a chronicle of the adventures of the eccentric Bagthorpe family: Mr. Bagthorpe, an irritable, paranoid scriptwriter; Mrs. Bagthorpe, juvenile magistrate and problem solver; their four children, William, Tess, Jack, and Rosie, all except Jack multi-talented; Grandma, the trouble-making matriarch of the clan; Aunt Celia and Uncle Parker and their four-year-old daughter Daisy, a pint-sized catastrophe waiting to happen; and Mrs. Fosdyke, the Bagthorpes' crotchety but talented cook.
These are hilarious books; I've read the first four at least ten times since I discovered them twenty years ago (the later ones are more recent acquisitions), and they still make me laugh out loud. The first four are the best; they're largely told from the point of view of Jack, the only ordinary one in the family, and his common sense and normality help to anchor the antics of the rest of the family. Also, there's a sense of family affection that's missing from the later books (though those are still funny and worth reading).