Hi there! I don't recall seeing your name around here before, so I wanted to introduce myself. I'm Lauren. I'm 27 w/CF.
A fecal fat test will show whether the pancrease is secreting enough lipase to break down fats in food. The other stool tests may be looking to see whether there's enough "good" bacteria in the gut. Things like E.Coli and other bugs may get out of control and cause problems, especially if antibiotics have been used recently.
A stool sample alone is not enough to give a definitive diagnosis or CF, but it will help give the doctors more clues and point them in the direction of what they should look for next (if anything. )
I hope it goes well.