I can easily see the British Government not letting Trump into the country, as unlike Boris Johnson, I don't think Liz Truss is a fan of his. Carter won't come because of his health, and I can easily see Hillary coming without Bill because of Bill's political woes (and the non-zero possibility he also gets barred from entering Britain).
Bill can sit next to Prince Andrew.
I highly doubt Prince Andrew will actually be allowed to attend either. Given the accusations against him, no one else in the Royal Family will want him there.
So you think the UK is going to ban two US presidents and THE QUEEN'S OWN SON?
OK, sure...
I'll point out that Prince Andrew wouldn't have been allowed to attend because of his Epstein links, especially since other members of the Royal Family are uninterested in protecting him.
As for Bill Clinton, I think he would be invited but Hillary (who presumably will also be going) will decide it's better for her reputation to leave at home in Chappaqua.
You have some, um, strange takes, that's for sure...