Well well well - at last someone from Portugal.
I have lisitng in Albufeira and have the same question.
Plus I am trying to figure out how to prove to my accountant Dona G. that airbnb is, in fact, paying IVA on the what they call "guest fees" which falls under "electronic services in Portugal" category.
Let me know if you find and answer (and if it is needed at all)
Logically - if you are property manager - airbnb is not the right place as they cater to individual owners, hence only single NIF in place