I usually base this on the hotel standards, as they’re pretty well-versed in the number of keys that guests need. Generally, they would provide 2 keys to groups of 3-5 guests.
That being said, I think this is really your own judgment call. In my experience, guests understand any convenience and safety precautions you may want to take…after all, it is your home. There are though, found here: https://www.guesty.com/academy/types-of-keys-other-specifications-for-airbnb-key-exchanges/. So if you have a sense that you’re disappointing your guests, you can always invest in another set.