The English translations for the given Spanish sentences focus on identity, emotions, and location.
Who is this man? is the correct English translation of ¿Quién es éste hombre?. In English, 'Who' is used when asking about a person's identity.
For the sentence How is this man feeling?, it is asking about the emotional state of the man. The word 'How' is used to inquire about the manner in which something is done or happens.
Where is your brother? asks about the location of someone. 'Where' is used when referring to a place or location.