It will be nothing like five figures for a fairly standard one-off 'something unfortunate that happened to us' book by two unknowns! You might get that if you were a celebrity memoirist who had a huge online following and/or the kind of fame that meant publishers could rely on having a built-in audience for, say, Graham Norton getting caught in an avalanche and surviving a week in a crevasse in the death zone while climbing K2, or in a world without NDAs or defamation law, 'I was a Kardashian Surrogate!' Or even if you were a recognised academic expert on something currently topical and with a big SM and TV profile who was reliably bankable. Say, David Olusoga on having a racist stalker will get a far bigger advance for a book about it, that an unknown person to whom exactly the same frightening set of events happened.
And most advances are now paid in thirds -- one third on signing the contract, one third on submission, one third on publication. But sometimes quarters, so the final quarter might not be till a year after publication. Publishing atm is all about risk mitigation.
But I'd be very surprised if the authors have made much money from this. It may have been optioned for TV or film, but even then, the big money won't come until/unless someone picks up the option, and the option could be quite small, depending on how eager a producer is to adapt it for screen. (And obviously, the negative response to the Guardian piece and the pulling of the book so close to publication doesn't bode well.)
A friend had her novel optioned by a famous actress turned producer who was very enthusiastic about it for years and kept renewing it for about eight years. It was never made. The option was something like £1k annually, or every 18 months.