A question about colloquial English

[Unregistered]

SCENE: A guard sees a man sitting in a seat exclusively reserved for people with disability. He may say the following to the man:

1-- Sir, you oughtn't to be sitting here. It is for people with disabilities only.

2--Sir, you oughtn't to sit here. It is for people with disabilities only.

3--Sir, you can't sit here. It is for people with disabilities only.

4--Sir, you are not supposed to be sitting here. It is for people with disabilities only.

5--Sir, you are not supposed to sit here. It is for people with disabilities only.

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Please tell me what is the best used sentence for that scene colloquially. Thank you.

[Soup]

3--Sir, you can't sit here. It is for people with disabilities only.

[joham]

Hi, Soup. Do you mean 'You can't sit here...' is the best answer? Then how about the others?

And how do the following two sentence with the 'oughtn't to be doing' structure sound to native speakers?
You ought not to be doing that, ...
" Curt, honey, you ought not to be talking like this, " Aunt Martha scolded. (Both from the COCA corpus)

Thank you again.

[bhaisahab]

Hi, Soup. Do you mean 'You can't sit here...' is the best answer? Then how about the others?

And how do the following two sentence with the 'oughtn't to be doing' structure sound to native speakers?
You ought not to be doing that, ...
" Curt, honey, you ought not to be talking like this, " Aunt Martha scolded. (Both from the COCA corpus)

Thank you again.

The other options are not wrong, it's just that Soup's choice is the most likely and natural in modern English.