Holy larp
"His 2 son's don't even talk about him in good faith"
Uh...yes they do? Let's break this down.
Dante: "No matter how hard you try, you're never gonna be like Father." (aka, righteous.)
Dante: "We are the Sons of Sparda, within each of us flows his blood, but more importantly, his soul." (His demon power but also the passing down of his ideals)
Vergil: "It seems our souls are at odds Brother."
Dante and Vergil both represent half of Sparda, Dante the protection of humanity and fighting for what's right, Vergil representing his demonic nature.
They both respect Sparda, just for different reasons.
Dante: "And now, my soul is saying it wants to stop you." (Sparda's ideals cannot allow Vergil to continue harming humanity.)