The true concept of Airbnb is people sharing their own homes (sometimes their second, separate homes) with guests. The company doesn't mind if a host has more than one property - this has been happening since the early days when a host might have two listings - one each for two bedrooms in his home.
Things are different now but nevertheless, the basic idea is that guests are dealing with their hosts (from enquiry stage through to check out time) if possible.
I look after our own rental and that of a neighbour. I have to log out and log in again - no big deal.The property owners have to create their own account, add their own photographs and their own verification. Airbnb runs largely on trust.
They can then add you as a co-host.