Immediately upon the death of Queen Elizabeth II, who will then be referred to as “Her Majesty the Queen”?

Legally Camilla, Duchess of Cornwall will become Queen Camilla. However this is likely to provoke backlash - people will say she doesn't deserve the title that should have been Diana's - 67% of people polled opposed her getting the title of Queen. Monarchies don't work like that though - you get who you're given and if you don't like i then tough. However, it's possible that she will not take up the title and be 'Princess (or even Duchess) consort'.

That's assuming Charles outlives his mother and will even become King. If not then it will pass straight onto Kate.

No one will be referred to that way until William becomes King.

The minute the queen dies charles is king,his wife camilla will be his queen consort, and as such will be queen, she may not be given the title her majesty, that has not been decided, they may just be called his majesty king charles III and queen camilla.

Assuming a normal order of succession, the current Princess of Wales (more commonly known as the Duchess of Cornwall) will become Queen. There has been some speculation that she will use some slightly less grand title such as "Princess Consort", but it remains to be seen whether that actually happens.

If the Queen outlives the Duchess of Cornwall, or outlives Prince Charles, the next Queen will be the current Duchess of Cambridge.

It would have to be Camilla, as wife as the new King

Nobody, the title 'Majesty' is used for the Monarch. The heir apparent will become 'His Majesty'.

Maybe Camilla or no one. It’s up to Charles to give her the title or not.

IF Charles is still alive he, and only he, will be announced as King - 'The Queen is dead, long live the King' and all that. I don't know when the situation with Camilla will be resolved, or how it will be resolved. That may have to wait until the period of mourning is over, and the next Kind crowned King in any case. Watch this space. Camilla will simply be acknowledge as Prince Charles' wife, immediately.

Queen Camilla will be called that by courtiers, servants, and all others once the current Queen dies

Camilla, but that will only happen after Charles is invested as King so it won't be immediately after Queen Elizabeth's death.