Will a person die when their name is written in the situation of death?
It seems this was actually confirmed by L in chapter 45. The Yotsuba company had made tests of their own, and deduced rules from this. One of the things they deduced was that


  If other names are specified, the action becomes void and they all have heart attacks.


Therefore a person written in the situation of death would completely void the action and kill all written names with a heart attack. Obviously the most fundamental rules need to be fulfilled (eg: Think of that person's face, nicknames would not work, ...), but it seems that the complete action would actually be voided if more names were written down in the situation of death.