It is a nightmare situation for the British royal and the former US TV star in the final hours before they tie the knot at Windsor Castle -- but one that many quarters say could have been prevented.
Markle's reclusive father Thomas is in hospital recovering from a heart operation, having been caught in a fiasco of his own making posing for staged paparazzi photos.
Her uninvited half-brother Tom Junior is hanging around outside the castle walls, while his ex-wife and children have also flown into London for their own merry-making reasons.
Markle's half-sister Samantha Grant -- also persona non grata, and also reportedly hospitalised after a paparazzi-dodging car crash -- has been venting forthrightly on numerous television stations.
The Daily Mirror quoted palace staff calling the marriage preparations the "Markle Debacle".
The entire scenario has left Harry's Kensington Palace operation under fire from all corners for failing to see it coming.
"Kensington Palace has missed a trick with the whole family," veteran royal biographer Penny Junor told AFP.
"The relatives have become a bigger story than the event itself, which is tragic," said the author of "Prince Harry: Brother. Soldier. Son. Husband."
"Kensington Palace could have despatched someone across the Atlantic to help them, give a bit of advice and moral support and prepare them."
She added: "I also suspect that Meghan missed a trick in not inviting her half-brother and half-sister to the wedding. Much safer to have them inside the tent than outside."
Newspapers have been piling into Kensington Palace for naively leaving Thomas Markle floundering.
'Shambolic' attitude
The Times columnist Jenni Russell said the palace "can't continue with this slightly disdainful, shambolic, cope-as-you-can attitude to those they co-opt into a circle of stratospheric fame".
She quoted a courtier as saying Kensington Palace "know they've dropped the ball on this. They're acutely embarrassed about it, and they're desperately playing catch-up.
"They're kicking themselves now."
Jane Moore, The Sun's former royal correspondent, suggested the palace should have read "media management for dummies" and stepped in months ago.
"It chose to ignore the speeding train heading towards the broken track," she wrote.
Moore said Thomas Markle should have been flown first class to Britain, put up in one of the crown's private cottages and talked through what to expect, with a photograph released of him with his daughter and Harry.
"The palace's failure to be pro-active has now necessitated a too little, too late reaction," Moore wrote.
Kensington Palace has been tight-lipped over the Markle crisis, refusing to go beyond its brief statements.
It is unlikely to admit any mistakes publicly.
Royal biographer Andrew Morton said the palace was a tighter circle than in the past, with fewer trusted staff in the loop due to the exceptionally cautious nature of Prince William, Harry's older brother.
"Kensington Palace like Buckingham Palace, is a place of rumour, hearsay and gossip. Essentially, what happens inside stays inside," he told AFP.
'He has changed'
Reports suggested Harry, 33, who is deeply sensitive to press intrusion, is very upset about what has happened to the father-in-law he has yet to meet.
Harry struggled to find lasting love, with previous girlfriends such as Chelsy Davy and Cressida Bonas feeling the scrutiny all too much.
Markle, 36, a self-made star and humanitarian advocate, is a polished performer who embraces the limelight.
But not so her family. Her father's absence on her big day has saddened her, according to her own statement announcing his non-attendance.
"He'll absolutely be hating it. He will be feeling guilty that all of this is happening to the woman he loves because of who he is," said Junor.
For years a reluctant royal, and thrown by his mother Diana's death in 1997, he has finally straightened himself out and embraced his position, realising through his Invictus Games for wounded veterans that he can use his status for a greater good.
Finding, at long last, the right partner to share his life and work with should have been the bookend to his turbulent youth.
"He has changed, he's grown up, he's matured," said Junor.
"Harry is in a really good place and heading in a very good direction at the moment. It would be terrible if this knocked him off that course."
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