If you own a company, that's not a job. If you are also the CEO and bring in half of the work/sales personally, that's obviously a job. The same person could be both, we all wear many hats, but even if you choose to call yourself the owner over CEO the CEO part is the job, the owner title is not a job

Collecting rent isn't a job. Maintenance is a job, and building is certainly a job.

If your dad is still doing maintenance, that's work. If not, I'd say he's retired, and renting out homes isn't the problem here

In this context, landlord means someone whose "career" is just owning a bunch of property. Unless your dad is a developer and "built" a bunch of homes by hiring a bunch of people and taking the profits, he doesn't deserve to be called a landlord, even if the term has been watered down

He rents out a room/house, after literally building it... That doesn't define him in the same way, he's not the problem and he shouldn't be painted with the same brush