A spokesperson for the California-based couple said this week there was no update on whether they were attending.
President Joe Biden, who will not be attending, told the King by phone on Tuesday that First Lady Jill Biden would represent the US at the event, the White House has confirmed.
"The President also conveyed his desire to meet with the King in the United Kingdom at a future date," a statement added.
Last week the King completed his first state visit, receiving a warm welcome in Germany. But the focus is now on preparations for the coronation.
Roles have been given to children of friends and relations, with eight "pages of honour" announced to take part in the ceremony.