They may have a rental property to file on Schedule E.     Read thru IRS Pub 527 Residential Rental Property.

Are you asking if their rental property qualifies for QBI?   

By the way you said "a second home someone lives in" it doesn't sounds like its being run like a business.

What "people" are living there?

If you're asking about QBI, the answer is no.  See Rev. Proc. 2019-38 Section 3.05(A).

Maybe it's like that Nicole Kidman movie The Others.   The ghosts don't know they're ghosts 😲👻

Is there some reason you call them "people living there," and not "tenants" ?   Do you call it a "home" and not just a "house" because he lives there sometimes, too?

Anyway, if you Google "Airbnb QBI" you find this interesting article:

https://www.accountingtoday.com/opinion/innovation-meets-regulation-the-looming-tax-headache-for-air...

Is this the same home you posted a couple of months ago? https://proconnect.intuit.com/community/proseries-discussions/discussion/i-am-in-a-nursing-home-my-d... 

Should you be wandering the TurboTax forum, instead of being here?

Does this return qualify as a simple return? https://proconnect.intuit.com/community/proseries-discussions/discussion/my-client-filed-a-simple-ta...