What is the ruling on kidnapping a man to ransom him for captured mujahidin, and is there a reward for the kidnapped person for the terror he experienced, and should he be asked for forgiveness if he turns out to be a Muslim?

If the man in question assists and supports the regime, then his ruling is the same as that of the regime's soldiers, and he is to be treated as they are treated, whether he is Muslim or otherwise. The crucial factor is his assistance in shedding blood and violating honors. However, if his arrest is due to his brother's loyalty to the regime, then this is an injustice that is impermissible, for Allah Almighty says: {And no bearer of burdens will bear the burden of another}. The oppressor must repent and seek forgiveness from the oppressed, and the oppressed will have a reward from Allah.