I called princess & they've told me that I could use 1 FCC for both myself & my wife but that her deposit would be higher & we would both receive the cabin credit.
That said, I have heard so many people recently saying both the same thing and the also the opposite so I've decided to purchase sufficient FCC on our next cruise to cover us either way. There seems to be lots of confusion, even from the Princess reps, as to the correct interpretation of their program. I would rather put out the extra $100 per FCC in order to get the cabin credit than be turned down in the future. After all it's only $100 per FCC & what can you actually do with $100 these days that can get back a return worth anything more.