@Emma-And-Oliver0 as soon as they book, or even better, before they book if you don't have IB on, ask them to book for the correct number of people since your apartment will ve set up only for that number and any additional guests will be denied entrance. If they lie and still come with extra people, make them alter the reservation before you let them in on check in day. If they don't want to, call Airbnb and have them cancel the reservation.
@Emma-And-Oliver0, in addition to @Ana1136's advice, I would raise the prices. Higher prices deter the kind of guests who are looking for ways to get away with things. Also - $67 and $39 a night for entire houses that sleep up to 11 people? That seems so low. Think about what it would cost a family of 6 to book in at a hotel - they would need two rooms - and put your price about 10% below the price of those two hotel rooms. It will be much higher than you're charging but will still be regarded as good value for the money.