When Melania Knauss, a Slovenian-born model, married Donald Trump in Palm Beach at 7pm on 22 January 2005, all was right with the world – at least in the eyes of the groom. At his wedding to wife No 2, Marla Maples, in 1993, only a load of B-listers had turned up. “It’s just like I was afraid of,” the radio star Howard Stern would tell a reporter. “I’m the biggest name here.” Now, though, Trump looked around and saw among those gathered at the Episcopal church of Bethesda-by-the-Sea not only Billy Joel, Barbara Walters and Simon Cowell, but also, infamously, Hillary and Bill Clinton. No wonder that once the vows had been exchanged he was moved enthusiastically to kiss his new wife three times in a row (the doomed Maples had received only a peck on the cheek).

Trump and his family set great store by appearances. Look beyond the surface of things, however, and whatever the occasion, you’ll find so wide a selection of cheap metaphors for the wobbly way their universe operates, you’re truly spoilt for choice. Shortly after midnight, at Trump’s Mar-a-Lago estate, the happy couple cut into their cake: a 70in, seven-tiered gold and white sponge, adorned with 2,000 sugar flowers. Weighing in at more than 90kg, by rights it should have fed the hundreds of guests with perfect ease. Only there was a problem. This mammoth confection was held together by a web of hidden wires, an intricate structure that made it all but impossible to slice. The crowd had to be fed specially baked back-up cakes. The real thing was only eaten later, once the party was over, by the staff.

Their lives, being all riches and no rags, afford neither reporter nor reader even the slightest change of tone or pace

Emily Jane Fox’s Born Trump: Inside America’s First Family fairly bulges with scenes like this; thick and fast they come, five or six to the page. If everything in Trump Land is flashy, super-abundant and wholly exorbitant, it’s also superficial, shoddy and almost entirely mean-spirited. At first, to put it mildly, this is queasy-making. When Trump flies in to Slovenia to meet Melania’s parents, a trip that lasts in total only a few hours – “I was there about 15 minutes…. I landed, said: hi Mom, hi Dad. Bye!” – you think all over again: my God, how ghastly he is. After a while, though, a certain numbness sets in. The news that Jared Kushner proposed to Ivanka Trump with a ring from her own jewellery collection barely raises an eyebrow. The fact that Donald Jr agreed to ask his wife, Vanessa, to marry him in front of a load of television cameras in a New Jersey shopping mall, in order to bag a discount on a $100,000 emerald-cut diamond, strikes you as so predictable as to be almost unworthy of comment.

This, I think, is one of the major problems involved in writing about the Trumps – and all the more so for a writer such as Fox, whose breathless prose is neither quietly angry nor laced with irony (a reporter at Vanity Fair, she is much given to the kind of glossy magazine talk that has her writing sentences such as: “They [Eric Trump and his wife-to-be, Lara] hired both a wedding planner and an event designer who worked with the couple to strike a balance between what Eric described as ‘formal and fun’ with elegance mixed in.”) Their lives, being all riches and no rags, afford neither reporter nor reader even the slightest change of tone or pace.

But there are other difficulties, too. For one, the Trumps have for decades lived out their lives in public, mainstays both of the New York Post’s Page Six and of reality TV, and thanks to this, Fox’s text often reads like nothing so much as an elaborate cuts job. For another, and this is perhaps the more important fact should you unaccountably be thinking of buying this book (I’ve read it so that you don’t have to), the Kennedys they are not. How unutterably stupid-seeming they are, and how unspeakably tedious reading about them is. From Fox, we learn, for instance, that Donald Jr’s nickname at university was Diaper Don, on account of the fact that in his frat boy days, he was inclined to wet the bed when drunk. His young brother Eric, meanwhile, was known by some school friends as Choad, a term that denotes a penis that is wider than it is long (good to know!). Ivanka, the oldest of Trump’s three children by his first wife, Ivana, used to try and make herself seem a touch more interesting than her brothers, and perhaps a little more classy, too. “My friends always joke that I’m going to marry a 90-year-old Pulitzer prize-winner,” she told a (baffled?) interviewer when she was still a single girl. But then she went and married poor little rich boy Kushner, whom even she once described as “a mutant”. What was on their wedding list? (Yes, they really had one.) Answer: 75 items from Williams-Sonoma, Crate & Barrel and Tiffany’s, among them some spatulas, a rolling pin and a Bundt cake pan.

Fox’s book is a gossipy family study; by design, it touches on politics hardly at all. Still, from her brief account of the transition, we learn that Trump wanted nothing to do with the team working on it (“bad karma”, he called the idea of his involvement, using a term he presumably picked up from Marla, who horrified him by giving birth to their daughter, Tiffany, surrounded by candles, with a Native American “nurturer” on hand to provide massage and prayers). Also, that on election night, it wasn’t only Melania who was seemingly traumatised. Asked for a kiss by her vice-president-elect husband, Mrs Pence – the poor creature whom we now know to call Mother – could only snap: “Mike, you got what you wanted.”

What does Fox make of the fact that Trump immediately tasked his son-in-law Kushner with achieving peace in the Middle East? Her analysis is bold. “Years of political know-how and understanding of an issue so complex that it has eluded seasoned diplomats for decades isn’t like conjunctivitis,” she writes. “It doesn’t rub off on shared pillows, nor is it picked up in conversations with a father’s friends over Shabbat dinner.” And having laid this matter thus to rest, she returns swiftly to the important stuff: Ivanka’s brief stint as a model and Jared’s Common Project sneakers; Tiffany’s tragically brief pop career and Eric’s excessive fondness for sauces; Donald Jr’s predilection for shooting prairie dogs in Montana and Donald Snr’s passion for the film Zulu. All in all, it fairly makes you weep, though whether from boredom or because no fewer than three of these people are now installed in the White House, it’s sometimes hard to say.

• Born Trump: Inside America’s First Family by Emily Jane Fox is published by HarperCollins (£20). To order a copy for £17 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99