Michael clambered down off of his bunk to face the open door, swinging lightly in the cold draft sweeping through the floorboards. Blake’s sheets were sprawled on the floor, as if he had scampered out of his bed. Michael knew much better than to follow his brother, because Renault would be out there. His father scared him, especially at night. Those knuckles, obscenely large for his frail hands. Those leering eyes, always spying on Michael and Blake. He knew that if he went out there, Renault would get angry, because he didn’t trust his sons. He trusted no one. All because of a Michael’s dead mother. But Michael couldn’t bear the thought of leaving Blake out there to his fate, alone. He had to join his brother out there, in the dead of the night.
So he walked out the door, cautiously and afraid, treading lightly, so as to not wake up Renault. His father would undoubtedly be sitting on the rusty red armchair in the main room, the only piece of actual furniture in the house. He had made it for Michael’s mother, shortly after they had settled in Aregont. She died the next night, with Michael in her arms. Renault hated him especially for that. But such hatred was ancient history. What really mattered was the present, and the eminent danger that Michael was risking.

EDIT: I gave the father a pronoun: his name.

There's just one technical thing getting in the way, and it's the use of pronouns:

Michael knew much better than to follow Blake, because his father would be out there In this sentence, we can't tell if it's Blake's father or Michael's father you're talking about. Don't write it so that we can understand it; write it so we can't possibly misunderstand it.

He had to join his brother Is Blake Michael's brother? Do we know that already? If not, then somewhere above you need to say, "his brother Blake" so we know when you say "his brother" later, that it's Blake you're talking about.

You get the idea.

ALso, does Michael have any relationship with his father's wife? I know I NEVER call my mom "my father's wife" -- how about you?

Here's one way it might look if you did that consistently with both characters. See if you think it reads more clearly:

Michael clambered down off of his bunk to face the open door, which wasswinging lightly in the cold draft sweeping through the floorboards. Blake’s sheets were sprawled on the floor, as if he had scampered out of his bed. Michael knew much better than to follow Blake, because Father would be out there. Father scared him, especially at night. Those knuckles, obscenely large for his frail hands. Those leering eyes, always spying on Michael and Blake. Michael knew that if he went out there, Father would get angry, because Father didn’t trust his sons. He trusted no one. All because Mom died. But Michael couldn’t bear the thought of leaving Blake out there to his fate, alone. He had to join Blake out there, in the dead of the night.

So he walked out the door, cautiously and afraid, treading lightly, so as to not wake up Father. Father would undoubtedly be sitting on the rusty red armchair in the main room, the only piece of actual furniture in the house. Father had made it for Mom, shortly after they had settled in Aregont. She died the next night, with Michael in her arms. Father hated him especially for that. But such hatred was ancient history. What really mattered was the present, and the eminent danger that Michael was risking.

He is absolutely terrified of his father. Imagine living with a thug. Would YOU give him a respectful title like "Father" or "Dad"?

He is so distant from his father that he does not even give him a title. He is simply "the father".

But very good points about "his father's wife". I'll change that to "his mother". She died when he was only an infant, and so, as he had never established any relationships with her, she is simply "the mother".

Thus, he does not call his father "Dad", for obvious reasons.

His father doesn't want the reminder that he has a son, so he tells them to call him by his real name.