As Kate Middleton will no doubt find, the Windsors really take the cake.
Gary Goldsmith, uncle of Kate Middleton, is a property developer who lives in La Maison de Bang Bang in Ibiza.
The only comfort for the Middletons is that this family from hell is not moving in next door.
To put it mildly, the career of Gary Goldsmith, the uncle of Kate Middleton, has had its ups and downs, leading to fears that the presence of Uncle Gary - Gary! - would cast a distinctly rough and common-looking shadow over the royal wedding.
Could the tattooed owner of La Maison de Bang Bang, Goldsmith's Ibiza home, be trusted, for instance, to mingle responsibly with guests including the Sultans of Bahrain and Oman? Would he undo all the good work of The King's Speech?
As if the commoner Middletons were not worrying enough to royal scholars such as James Whitaker, there had to be a risk that Goldsmith, a property developer, might, with his record of upstart hedonism, actively contaminate an occasion featuring a King of Saudi Arabia, Tongan royalty and the hardly less eminent royal broadcaster, ITN's Tom Bradby.
Goldsmith's failings were not, like the Middletons' table manners, a matter for nervous conjecture, they had been recorded on tape by the News of the World's fake sheikh, this time posing as a businessman.
Goldsmith had said, for example, that his first words to Prince William when he came to stay were: "Oi, you f*****, did you break my glass pyramids?" (Goldsmith collects glass pyramids.) In mitigation, Goldsmith was hospitable to a fault.
He had, as an internet search will show, offered the reporters cocaine and the number of a pimp.
As it is, after various acts of contrition, Kate Middleton's uncle, her mother's brother, will after all be invited to every part of the event, as will all her fiance's uncles, Prince Edward, Viscount Althorp and, at the time of writing, Prince Andrew, companion to eastern European tyrants and, when in America, the paedophile Jeffrey Epstein and his alleged procuress Ghislaine Maxwell.
Risky, perhaps, but at least it will be someone for Andrew to talk to.
And yet Goldsmith must be wondering, their legendary rudeness aside, does he really want to mix in this company? True, William appears to be a thoroughly white sheep and has overcome dreadful setbacks, but what can you say about his relations? Goldsmith is rich.
What if a royal attempts to touch him for a free holiday in Ibiza, or even a loan? It happened with Epstein, who paid £15,000 ($33,315) towards Sarah Ferguson's debts.
At this wedding will be at least two of the Windsors' financial incompetents, currently known to include: William's aunt-in-law, Sophie Rhys-Jones, whose RJ-H PR company left debts of £1.7 million; another aunt-in-law, Sarah Ferguson, whose creditors have subsidised her £5 million losses; lastly, William's uncle, the Earl of Wessex, whose investors were left with nothing when his film company, Ardent, went into voluntary liquidation, with assets of £40.
Then there is the question of Mazher Mahmood, a person Goldsmith might want to forget. How can he when Kate's new family again features three of the fake sheikh's celebrated victims: Sophie Rhys-Jones, Sarah Ferguson and, in 2005, Princess Michael of Kent, who confided when Mahmood posed as a potential buyer for her house, that Charles had, in William's mother, married "a womb". If Mahmood bought, she told him, by way of an inducement, she would open a supermarket in Dubai for £25,000.
But Goldsmith's misgivings must be as nothing compared with those of the Middletons. Yes, Kate is 28 and must think for herself, but it is only normal that decent parents like this, strangers to both bankruptcy and dependency, would wonder until the last minute if there is a way to stop their personable, carefully educated daughter marrying into a family where everyone, including the older males, relies on handouts from an elderly matriarch or the state.
Hardly surprising, given their lifetime of dependency, that so many of William's relations have become resentful, infantilised, irresponsible.
Not just Andrew - one thinks, in particular, of Princess Anne, repeatedly convicted for speeding, and once for owning a dangerous dog, Dotty, which having been acquitted in court of canine "malice" after biting two children, went on to kill one of her mother's corgis.
That William's father does not so far as we know have any similar record cannot be much comfort.
Prince Charles' alternative thinking is harmless enough, until she falls ill, and no doubt William will prove a more reliable husband. A passion for Saudi Arabian royalty is less easily ignored. We can only speculate on why British royals are so dazzled by princes from despotic, corrupt, viciously misogynistic Arab states in which the routine torture, public executions and repression equal anything witnessed in the English middle ages, but the family weakness has certainly made life easier for Mahmood.
For Kate, though, these tyrants will become cherished family friends.
Factor in the Windsor family's divorce rate, its binge-drinking princesses, racist grandad and trashy uncles, and the only comfort for the Middletons is that this parasitic, ferociously right-wing family from hell, emblematic of so much that is amiss with Broken Britain, is not moving in next door. But that is only half of William's genetic inheritance.
Possibly his non-royal uncle Viscount Althorp's company will prove more congenial to a family such as Kate Middleton's. It was Charles Spencer who pledged as Diana's "blood family" to let William and Harry's souls "sing openly".
It still remains to be seen whether they will rival his own, uninhibited example - two marriages followed by two engagements, the second still scheduled for consummation in June.
On the other hand, Spencer has no known connection with any dictators or sex offenders and is thought once to have worked for a living, making him very nearly respectable.