Our feature artist/ref today is on FORESHORTENING ARMS by @ruchikapose! The MID-POINT of the arm ( here marked with WHITE bands) SHIFTS BACK VISUALLY when foreshortening - combined with the OVERLAP caused by the WIDTH of the upper forearm, we see VERY LITTLE of the UPPER ARM!
First, breathe. You're right, there is no reason to feel guilt for killing. Sometimes, that's survival. Your brother's remorse would hinder his ability on the battlefield, so killing him might even be mercy. You're considering his strengths, and, honesty? that's caring.