@Tselane0 . If you want help from AirBNB you will have to contact them directly using the telephone, twitter or facebook. AirBNB customer service doesn't monitor this community board.
Just had a look at your listing, and it looks like there isn't an additional charge for your second guest but there is for your third and fourth. Which is rather strange.
Do give Airbnb a call and ask them to help you. All the ways of contacting Airbnb is in the CONTACT AIRBNB post towards the top of the Help Forum.