Why not "porcii ai săi"?
I have the same question.
Maybe "ai săi" is available only after verb. As subject it seems to be only "săi"
Why not să but lui?
I think you could equally say ”porcii lui” or ”porcii săi” (the latter could also mean her pigs) but ”sa” is singular and does not agree with the plural noun ”porcii.”
What do you mean?