1) This is a matter of disagreement
Ayatollah Jafar Amili who has written one of the biggest biographies of the Prophet (over 40 volumes) concluded that the prophet had one daughter only. I agree with this and evidence points to this, such as praise of sayida and no praise of other 3 for eg
2) It’s because of his adopted daughters. They were daughters of the sister of Khadija Hala.