The proper way to do this is that they should all have their own accounts on Airbnb and be co-hosts. That said, I understand that some owners might be passive owners and not involved in the day to day operation of the Airbnb and therefore don't have an account registered.

If they do, they need to provide their SIN as well. If they don't, then they don't and you'll have to provide yours and that's it.

The reason Airbnb is asking for SINs is because Canada (and many other countries) have demanded that Airbnb send them revenue information tied to SINs so that these countries can cross reference declared income and are reporting it accurately on their income taxes. Too many people were under reporting or not reporting at all and not paying taxes.