there may be an easier way to do this. but we can simply do this by cases.
Assume Anabelle is telling the truth. then Zay's statement is false, Gustavo's is true, and Deidre's is true. So in this case, only one statement is false, so this answers the second question.
now assume Zay is telling the truth, what does that mean? what about if Gustavo is true? or Deidre?