To ferment (inoculate), your father depended on the indigenous yeast, which was floating in the air. Many commercial wineries do the same; for instance, several Malbec producers in Argentina.
However, with trials, they know that the yeast will do the job properly.
You, on the other hand, may or may not know anything about the indigenous yeast in your area, so you could be taking a really big risk, if the yeast is not what you expect. In some experiments I have read about, the wine turned out so bad that it was not drinkable.
Using packaged yeast will let you know before you ever start what the yeast are expected to do.
Here's what I would do:
Experiment!
Start a small sample using indigenous yeast.
For the bulk of your wine, use a packaged yeast until you determine exactly the outcome of your indigenous experiment.