@Gillian120
if there are more people then booked then you are not obligated to host them. Do not let them in before they accept/pay extra fee for extra people
Or you can contact Airbnb and make them cancel the reservation
I would strongly advise you to charge for infants (put it in your house rules) to avoid such situations.
If your listing is family-oriented you may think of the possibility to remove laundry machine from your amenities or to buy coin-operated model. Hotels don't offer it for free either.
I will never forget the amount of laundry I had while my daughter was a kid, it was fascinating.