The Queen will meet senior royals in Sandringham later to discuss the future roles of the Duke and Duchess of Sussex.
Prince Harry, the Duke of Cambridge and the Prince of Wales will all attend the meeting, while Meghan is expected to join the discussion by phone from Canada.
The Sussexes say they plan to step back as senior members of the Royal Family.
BBC royal correspondent Jonny Dymond said a deal “might take time”.
It is hoped the talks will produce a “next step” on the way to defining the couple’s new relationship with the Royal Family – in line with the Queen’s wish to find a solution within days.
Among the issues likely to be discussed are what funding the duke and duchess will receive, whether they will keep their titles, and what royal duties they will continue to carry out.
Prince Charles has returned from Oman for the talks after attending a condolence ceremony following the death of Sultan Qaboos bin Said Al Said.
Prince Harry is understood to be travelling to Sandringham from Frogmore Cottage, his home in Windsor.
In their statement on Wednesday, the couple said they intend to “step back” as senior royals and work to become financially independent.
They also said they plan to split their time between the UK and North America, while “continuing to honour our duty to the Queen, the Commonwealth, and our patronages”.
Monday’s gathering at the Queen’s estate in Norfolk – being described as the “Sandringham summit” – will be the first time the monarch has come face-to-face with Prince Harry since the Sussexes’ announcement, which was posted on their official Instagram account.
The Queen, Prince Charles, William and Harry are expected to review a range of possibilities for the Sussexes, taking into account plans outlined by the couple.
If a deal is agreed in the coming days, there is a general understanding that it will take some time to implement.
Newspaper reports suggested the couple could conduct a potentially damaging television interview if they were unhappy with the outcome of the discussions.
Broadcaster and friend of the couple, Tom Bradby – who made a documentary with them last year – wrote in the Sunday Times: “I have some idea of what might be aired in a full, no-holds-barred, sit-down interview and I don’t think it would be pretty.”