After Musk first bought around 9% of company, Twitter used so called poison pill, which would deny Elon to buy more than 15% of company’s stocks without an approval of the board. However, even if the company now is in talks about the potential selling, it does not mean that parties will come to an agreement.
Elon was meeting with other shareholders in the past few days, seeking support for his offer. He also added that Twitter should be taken private in order to succeed and implement free speech. Company also did not like his statement, that the offer of 54,20 dollars per share is final and best. They are hoping that he will be able to adjust and offer to their favour.
Twitter, before making any rash decisions, will first try to find out if Elon Musk has any active investigations by regulators, including U.S. SEC (Securities and Exchange Commission). They will also tr to find out if any major market opposes Elon buying the company. They simply want to avoid any complications in case they decide to sell.

Movement of Twitter in the last five years. (Source: Trading Economics)