(2-5)  To you it’s simple. Vlad and Margaret are not moving relative to you and they are at equal distances from you, so they will see the light at the same instant: 

To Nefertiti, however,  it looks more complicated because everyone is moving relative to her. So as the light starts its journey in opposite directions, Vlad is moving towards the light but Margaret is moving away from it. Since light travels at the same speed in any frame of reference, this must mean that by the time Margaret sees the light, Vlad is already well accustomed to it:

No doubt "yes but…” is already forming on your lips but remember Uncle Albert is at your shoulder: the speed of light is the same in any frame of reference, and in Nefertiti’s frame, Vlad’s coming to meet it, so he’s going to get it quicker.

So what this teaches us is that events that are simultaneous in one frame of reference occur at different times in another frame of reference …….