And he's the one that made him marry stella in the first place

Probably not care.

He would probably just say "holy shit" in such a casual tone like he doesn’t care about his son one bit

Assuming that Paimon has some shred of affection and concern for Stolas (which I highly doubt)... and from what I've researched about the mythology related to Paimon... he would go straight to Lucifer's palace... to try to talk to Lucifer.

Paimon would go to the palace gate and wait for someone to open it so he could go talk to Lucifer. But no one would show up and he would give up on the idea of ​​talking to the entire king of Hell to take Stolas's sentence away.

Mythologically, Paimon's origin is this:

Paimon was once an angel of God and belonged to the order of Powers whose former name was Umbriel, but was persuaded by Lucifer to side with him in the rebellion against Heaven. With the defeat of Lucifer and his rebellious angels, Umbriel was thrown into Hell along with the other rebellious angels by the archangel Michael, he lost his angelic aura and became a demon called Paimon. He is one of the most loyal demons to Lucifer.

He probably wouldn't care tbh

"Who's Stolas"

Does he even know? I doubt he cares anyways

He would not care in any way shape or form.

"What son?"