But Samantha has accused the couple of inviting "complete strangers" - and claims "no one" from the Markle clan made the coveted guest list. "Exclude the [Markles] from this wedding would be highly inappropriate", Grant tweeted on Thursday.
More than 2,500 members of the public have also been asked to help celebrate the big day.
51-year-old Grant, who is confined to a wheelchair due to multiple sclerosis and lives in Ocala, suburban Florida, with her husband Mark, has previously said the princess-to-be has abandoned their father, Tom Markle, who filed for bankruptcy in 2016 and now lives in Mexico.
"At issue is not a matter of closeness as more than 1000 complete strangers are invited".
It's not yet known if he'll walk his daughter down the aisle.
Meghan Markle and her mother Doria Radlan watch the closing ceremonies for the Invictus Games in Toronto, Ontario on September 30, 2017.
Apart from majority of citizens, some well-known names were expected to be invited to the wedding but are not.
"No one has one yet".
"Well, everyone is making arrangements and it's hard to organise everything as you can imagine".
The couple is due to Wednesday on May 19 in a ceremony that will attract media buzz, as it is accustomed to royal weddings and the debate the union created in the media.
A Kensington Palace source confirmed the Obamas would not be attending and said the wedding guests would be people who have an existing direct relationship with the groom or the bride or with both.
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On the guest list includes, Amelia Thompson, 12, a school girl who survived the Manchester bombing.
Memorabilia with the royal couple's engagement photos started doing the rounds of the nation's markets soon after the official announcement.