@Silvina120
Agree with you. Pet fees should be set at per pet/night basis. This is one of the things that Vrbo has figured out and does.
Some Hosts explain on their listing the pet fee is for 1 pet for a max of XXdays. If you accept more than one pet, or you want to charge a higher fee for longer stays, you will have do process the guest payment before arrival via the resolution center. You will have to make this clear on your listing and in your House Rules and be sure to stay on top of that though, as many guests won't want to pay the addl fees. I would message them after booking confirming the number of pets and explaining they will receive a request to pay via the resolution center and it must be paid before arrival.