@Sean44
Just an idea: Use the basic rental fee for 2 ppl and charge an X amount for each guest extra.
If you are in communication for somebody who wants to exceed the 4 max and it's not a problem for your insurance or city regulations having more guests, you can do the following to amend your reservation:
Change the max guest settings of the listing to the no. you need;
Change the reservation and your guest will have to accept it.
Right after change has been sent off, you go back into settings and revert to 4 ppl. maximum.
The reservation change won't be affected since reverting back was done after the fact.
Playing around with the settings like that make it possible to accept diverse guest wishes if so desired, but work only after communicating with you.