I'd say it means that it matters a lot (much) to come from a good family, but it isn't everything. Other things matter too, such as good friends or a satisfying career. I don't know if that interpretation makes sense in the context of the book, but it's his it strikes me in isolation.

I've taken a step back from this confusing phrase, and I think I know what she is trying to say. In the paragraph that follows, she goes on to say that the best families are those whose members have outside interests. 'Everything to none' means that there is no single member of the family for whom family is 'everything' - all family members need to have interests and passions outside the family unit. Ms Howard seems to be the type of journalist who is determined to preface everything she says with a succinct and pithy quote. Unfortunately, this is one that doesn't really work very well.

How do you understand "Good families are much to all their members, but everything to none "? With great difficulty, frankly. Good families are much to all their members, but (good families) are everything to none (of their members). I really don't know what this means. I have found the original quotation written by the journalist Jane Howard around fifty years ago, and it doesn't even make much sense in the context of her book. Here it is: http://aplang2011.edublogs.org/files/2010/07/01howard.pdf