First of all, please replace all semicolons with periods.
Second of all, you don't need to use multiple exclamation marks to express one's frustration or other strong feelings (such as your case) or to show emphasis.
Here:
"Too slow", yelled the man before dropping the wooden training sword and placing his hands on his hips cloaked in armour,
The line 'placing his hands on his hips cloaked in armour' sounds somewhat awkward and forced. Maybe you could say something like: "Too slow," yelled the man in armor before dropping the wooden training sword and placing his hands on his hips.
Here:
"You would be dead if this were a real fight. You have really improved; you are far more agile than last time and could beat most men in the army!"
I understand what you meant, but it is not totally clear. Maybe you can rephrase it like this: 'You would be dead if this were a real fight. However, you have really improved since last time. You are far more agile and could beat most men in the army now.'
Here:
"But Sir, please, it's so boring on the farm; I don't want to end up like my Father!! I want to be of use and fight; I know we need fighters after last week's attack on that local mining town Thorpes," he replied out of desperation.
Maybe, you can say it like this: "But Sir, please! It's boring on the farm. I don't want to end up like my father!" said William in frustration, his face twisting, "I want to be useful and fight. I know we need fighters after last week's attack at the local mining town, Thorpes," he continued, despair visible on his face.
Here:
He picked up his Father, covered in manure and hay and tried to hold his weight to get him inside the house.
It seems a little forced and paced without a purpose. Maybe you can add a comma after 'and hay'?
Here:
"Put me down, Will; I'm fine, stop. I don't want Alina to see me like this..." slurred his Father as William closed the barn doors before turning to his Father, who had sat down on an old tree stump which he had once cut down.
Repeating the word 'father' twice is not actually necessary. You can say it like this: "slurred his father as William closed the barn doors before turning back to see him sitting down on an old tree stump which he had once cut down."
Here:
Picking up his Father, "You need to sort yourself out and stop drinking so much; mother needs you to help us both."
I mention this because it made me confused the first time I read it. You forgot to add something like: Picking up his father, he said harshly, "You need to sort yourself out and stop drinking so much; mother needs you to help us both."
Here:
Dropping his blacked-out Father on the floor, William hugged his Mother and went to his dark room lit only by a small candle on his cabinet.
I understand what you wanted to express here, but it is not totally clear. Maybe you can rephrase it like this: 'Leaving his blacked-out father to fall on the floor, William then hugged his mother before going to his room, lit only by a small candle placed on the cabinet.' or 'Leaving his unconscious father to fall on the floor, William then hugged his mother before going to his room. The only source of light aiding his sight came from a small candle placed on the cabinet.'
Here:
William laid back on his bed and stared at the wooden beams holding the thatched roof above his head, dreaming of a future he could have as an influential leader and warrior.
Again, I am mentioning this because it made me read it twice. Maybe you can rephrase it like this: 'dreaming of the future in which he was an influential leader and warrior.' or 'dreaming of the future he could have as an influential leader and warrior.'
Here:
William heard the usual shout from his Father to his Mother and then the inevitable smack and thud on the floor. A single tear escaped his eye but was quickly wiped away when he felt the cold, wet drop slide down his freckled cheek and the knocking at his door.
The way you wrote this doesn't match your past writing style. Maybe you can write the first phrase like this: 'William heard the usual fight between his parents, followed by an inevitable smack and a thud on the floor.' or 'As always, he heard his parents arguing, then the inevitable smack and thud on the floor.'
Here:
He was no man; he was a monster. He saw red.
I understand what you meant here, but it seems awkward. Maybe you can write it like this: 'His humanity was no more. He became a monster. He couldn't understand what was in front of him anymore, being able to perceive only the red shade of blood.'
Here:
"I forgive you, don't worry," William said as he comforted his Mother by putting his arm around her
It seems passive and superficial. Maybe you can describe his inner thoughts? Something like this, perhaps:
"Listening to the story, he could grasp both the sadness and the misery of his mother.
"I forgive you. Don't be bothered, mother," said William as he placed his arm around her waist, reassuring her."
There are other things I spotted, but for this chapter, I will stop. You get the idea.