OP - you keep saying both 'news reports', 'articles', or people on Mumsnet are reporting that the Wales' are doing this, the Sussexes are doing that or not doing that. It doesn't matter what 'royal experts' and randoms on the internet are guessing. At this point no one knows what any of the children are actually going to be doing.
At this point the only official announcements have been this:
There is going to be a ceremony with some members of the royal family present.
There is going to be a procession with some members of the royal family involved.
Everything else is rumour and speculation - all the articles say things like 'expected to' etc. The palace has not released any statements about who or who has not been invited in respects to the Sussex family.
A spokesperson for the Sussexes has said that they had received some information by email but have not confirmed their reply - no mention of the children but doesn't mean they have or have not been invited, or they are or are not going.
From The Guardian:
"A spokesperson for the Sussexes said: “I can confirm the duke has recently received email correspondence from His Majesty’s office regarding the coronation.
“An immediate decision on whether the duke and duchess will attend will not be disclosed by us at this time.”
https://www.theguardian.com/uk-news/2023/mar/05/harry-and-meghan-have-been-invited-to-coronation-spokesperson-indicates
Here's the government's official Coronation site. If you can't find the news on there then it's all speculation at this point.
https://coronation.gov.uk/
Here's the only official statement released by the Palace:
https://www.royal.uk/coronation-weekend-plans-announced