I very much agree. I find myself shifting back and forth between the MC's father being the 4th serpent or not.
There are some things that just make me feel iffy either way, like Trino gets a bullet to the head right there and then and that's for relaying a location. And yet both the MC's father and mother are still alive and kicking.
From what we've been told, they must have done something so out of the world fucked up, that they were not just exiled, the DeLuca's and Pacifactories conspired to keep it a secret and forged documents and shit, like how the fuck are they still alive ?
And what bothers me the most is, that people regard Rina with compassion and they all hate the MC's father. I sometimes just can't believe that cheating would do it, although Antonio being the MC's half brother would be amazing.
After replaying the game, my opinion is that the 4th serpent isn't the father. I will detail my thoughts.
If everyone from the Deluca family hate the father, it could be because he is the Silverino Don (Nero also ressembles MC quite a lot). Since this Silverino family is depicted as manipulative and conspiring, they could have had a big plan to merge one of the strongest family (Deluca) with them by having a heir from both family. Quinzio states that MC has a role from Silverino family, which would be this one.
Rina would have been the "true" heir of DeLuca Family (or at least a candidate), giving the MC the possible right to reign over 2 big families. Silverino would absorb Deluca and grow their power and influence by a big margin without having to start a war.
Other families would have heard of this plan and of the child (MC) and decided to eliminate him to prevent this merger that would break the balance and Rina's pregnancy with an enemy don would have been seen as a betrayal from Deluca family. With assassins sent on her tracks by other families and no support from Deluca's Family because of her betrayal, she would have killed lots of people, including big shots from different families, explaining her exile from the underworld.
Before leaving peacefully without more blood spilled, she would have signed a contract with Pacificatori and Deluca and Silverino to ensure her and her child (MC) safety by saying that her child would go back to the Deluca Family and be protected by Silverino from afar after a certain age. Being one of Deluca's potential heirs, it explains him being in the mansion, wilfred speaking to him like a core family member and protected from afar all his life. His mother would have been harsh on MC to prepare for mafia world to ensure his survival in this world.
This would also explain why DeLuca watch MC from a long time and why Wilfred kind of gives vibes of wanting to see how MC grows as a leader and potential future Don. Wilfred is very cunning and plans on very long-term. By using MC he could make the Deluca Family grows at the top, explaining also why he lets MC be close to the sisters, to make MC fond of Deluca's side and not his father side (Silverino).
Concerning future events, MC already has a team of competent people around him and this team could have some logic. I had this thought on the Fawkes kidnap mission after saving him from the car where you get to chose a line to tell him he is a nice guy. MC's position and the others around him gave me this birth of a "new family" vibe. He could create his own group which would be Deluca based but with addition :
Leader : MC
Consigliere : Gracie (Top strategist like Wilfred with good physical potential)
Serpents level : Luna (being Luna
), Fawkes (potential since MC seems to have gain his respect), maybe others in the future
Assassin unit Capo : Eiza (good potential if well trained)
Stealth Unit Capo : Joey (in stealth unit)
Intel unit Capo : Siobhan
She is a potential ally since from Story 11, we see that she respects MC and MC probably triggered her will to become next Ombra's heir to change her family and not just suffer the situation from their discussion during the warehouse attack. She also states that she wants to reform the Ombra's family and have principles which MC have also shown (not using any relatives or innocent people...) and since Efrem's code live within Eiza and that MC is Eiza's boss... It is possible she would also become an antagonist but it is 90% chance to become an ally in my opinion.
MC also has Elektra's support that could become interesting in the future inside the Family. He also seems well appreciated from support people like Gina, Bianca who seems friendly.
I saw comments saying that Gracie would become heir with MC as consigliere but I think he has more the Don type of approach than Gracie. He reads very well people which is Gracie's weakness.
In my opinion, it wouldn't be a coup d'etat in Deluca's Family but a generational change. Antonio doesn't seem fit to be next Don, he undeniably has potential to be the 3rd man of the family but lacks the strategic and cunning side to be a successful don of the family. Cordia would give him the Don position and retire from the first plan.