Question: What sickness does the king have, which he apparently succumbs to at the end?
Question: What illness does Robert's father have?
Answer: Within this movie's storyline he has leprosy.
Question: The Irish man uses the "F expletive" in one of his first scenes. Would that word have been in existence then?
Answer: It might have as the word is very old. But since it has always been considered very obscene it doesn't appear much in written form (before modern time). The earliest written occurrence known is in a poem from before 1500. But regardless of whether the word existed or not; the dialog in Braveheart is in contemporary English, since 13th century Scottish would be impossible to understand for the average moviegoer. So it's not a mistake for a character to utter the f-word.
Answer: There's also lots of f-words in Luc Besson's The Messenger: The Story of Joan of Arc by The English Commanders.
Question: Why does Wallace spit out the pain killer that the princess gives him?
Chosen answer: Just like he said, it would dull his wits and not leave him fully lucid the next day when he had to face the torture.
He wanted his full awareness so he didn't accidentally yell for mercy.
Answer: Because it's a reference to what his Father's last words to him were at the beginning of the film before he was killed, 'I know you can fight but it's our wits that makes us men'. That's why Wallace says to the Princess, 'It will dull my wits and I must have them always'.
Question: Why did they decapitate Wallace after he said "freedom"? I thought they implied that if he said "mercy", they'd give him a quick death, but if not, they'd continue to torture him. So what would they have done if he said "mercy"?
Answer: In the end, they just gave up. They realised he was not going to say it before dying anyway, so they ended it. If he would have said "mercy" they would have done the same thing, but it didn't matter anymore. They couldn't break him.
Question: Directly before Wallace is beheaded, he sees his dead wife in the crowd. Is this meant to be her ghost or is he imagining it?
Answer: I prefer to think that her spirit is actually there to welcome him to the afterlife.
Its all left for us to figure it out.
Answer: He is imagining it. He is trying focus on the fact he will see his wife again soon, in the after-life, rather than the pain of torture and his impending death.
Answer: King Edward I died of dysentery.