Hi @Lisa-and-Dean0 I hope you are well!
Of course you can ask your guest to confirm the number of guests in their party- I am sure they will be more than happy to clarify that for you 🙂
If you don't hear back from the guest, or you do and you're uncomfortable with the reservation, because you use instant book you can contact Airbnb CS and cancel if you need to- I'm sure you won't need to though.
Do not ever cancel yourself from your end without consulting with Airbnb first though as this could leave you with penalties you don't want.
A polite and friendly chat is usually enough to put your mind to rest if you're not sure about a guest or a reservation.
Hope all goes well.
Paul 🙂