Let's say, the first user is editing the page and if the second user attempts to edit the page the same time, it should prompt some sort of message that the second user will have to wait until the edits from the first user are complete. In other words, the second user should not be allowed to edit the page until the first user saves the edits.
And when the first user clicks on the save button. It generates a slack or email to the second user informing that the first user is done editing the page.