1. Why will they hold a party?
2. When will they hold a party?
3. Which party will they hold?
4. What kind of parth will they hold?
5. They will hold a parth for their teacher's party.
[#5 is the answer to the questions from #1 to #4. Which questions are suitable questions for #5?]
#5 will be fine if you don't repeat "party."
They will hold a party for their teacher.