Just as afterthought, I personally would inform the guest to contact Airbnb to provide such confirmation or any details regarding visa applications. You are the host not a friend or family so you don't really know these people is it wise to provide anything other than that which you can both print off the platform. They can provide supporting bank statements as evidence of the money they have paid to Airbnb for the accommodation or paid to the main guest as a share.
The main guest could also e-mail you via the Airbnb platform confirming the full names of the additional guests who will be staying in your property and confirm that they will show passport as evidence of identity on arrival. You can then respond confirming that you acknowledge that the reservation for XXXX (dates booked) by XXX(main guest’s name) , that the additional 2 guests permitted to stay in the property along with main guest during the duration stated above are xxxxx (list names) and will be subject to all house rules, listing description and Airbnb T&C’s as apply to the main guest. Unless Airbnb is able to provide an alternative confirming all their names, they will just need to print off the e-mail along with the main guest’s booking reservation and BK statements and take it from there; any further issues they have to refer to Airbnb to assist.
