How would you handle answering a phone caller's question with five lines ringing?

First, take a big breath. Introduce yourself and ask if they can hold. Keep a list of who/what the issue is on each line. Transfer each call as quickly as you can, and then return to each line in turn. Probably with five lines, it is not your responsibility to provide thorough answers--it is more to transfer that call to someone who has the time and expertise to answer.