Im trying to figure out was it necessary for the uchiha to take their family members eyes. Couldn't sasuke and itachi just exchange eyes and have the same effects as taking them away without the lost of a life, we've seen izuna give his eyes to madara even though he was dying and madara was losing his light but izuna gave them to him and died after. So my question is was it witnessing the death of their brothers or receiving the eye itself that gave them the power up or is a combination of both necessary for the full potential of the sharingan to awake