The first playthrough we should experience the “tragedy” side of it and require the marriage and the killing of the father. Get achievements for the uneasy things.
Here’s my twist:
On subsequent playthroughs, if the achievements is already there, then a new set of options will appear in the choice tree, including an option not to get married, an option not to kill the father, and an option to fulfill your fate without fulfilling your fate.
The third one is a bit hard to do. I’m thinking something like… if fate cursed you to marry your mother, then you can “marry” her, but not in the literal sense… work with figurative meanings to find a way to fulfill fate but not in a terrible and gross way. For example, I think the dynamics of attraction need to be greatly expanded and worked through; give the MC choices that allow him to think about WHY he is attracted to her. Some of this is already there: reasons of power, or control, etc. Those type of reasons need to be supplemented with a “well, I don’t really need to become her actual husband, I can just become her chief advisor and rule from the shadows.” That sort of relationship is intimate enough to be considered a marriage because you would become entrenched, so to speak, in the work. There should also be several options that allow the MC and his mother to get to know each other better, non-sexual options that explore and nurture several different kinds of attractions based on what the player chooses. Perhaps the love or admiration the MC has for his mother is something that, through a series of choices, the player can “untwist” or in other words, either break free from the curse, or reveal the true strings of fate that have been woven for Oedipus.
Dealing with the father so that he doesn’t die…, huh? Alright. For that, if you have the achievement from last playthrough, you could meet him in that dream sequence that shows him when he was younger but this time you could actually talk to him and, depending on what you say, alter the events of the past. If you make a strong enough case that you have no choice but to fulfill your fate and then somehow mention that it feels like you already did fulfill your fate in another life (talking about the achievement without breaking the 4th wall) then perhaps you can get another god to sponsor you and actually allow you to change the past through the dream. I’m thinking Nike, goddess of justice, would do well here.
Doing something like this would allow you to be true to the original, and also allow you an opportunity to redefine the tale for a contemporary audience.