She insisted

  1. She insisted that they give her a receipt.
  2. I demand that he leave at once.
    Are the sentences correct?


I would say ‘leaves at once’ in number 2 (Alternatively ‘…that he should leave at once.’). They are legitimate (and more natural) shorter forms of:
She insisted of them that they give…
I demand of him that he leaves…

In reality, I think I would also say “leaves” in conversation. In formal writing I think I would use “leave”. I think I remember reading somewhere that AmE speakers are more inclined to use the subjunctive (“leave”) more consistently than BrE speakers in such cases.

She insisted that they give her a receipt.
Here the formate of the bold part is present simple but sense is past. am I correct?

she insisted (in the past) that they give her a receipt (at the time that she asked).

It is not present simple but subjunctive.