Yes, there are some good PVP's at Carnival. And if you happen to get lucky and find a good one, stick with them. But as my Carnival Business Development Manager once told me, the average lifespan of a PVP is less than 6 months, so the majority of them aren't there very long. However, that's just one cruise line. If you want to look at everything else that's available, that Carnival PVP can't help, which is why it's always good to have a great working relationship with an agent who can look at all the cruise lines. (And yes, I'm obvious biased on the matter.) But having been involved in travel for over 25 years before starting my own company 11 years ago and knowing what I know now, if I weren't in the business, I would always let an agent do the work for me. Just not worth all the time, hassles, and stress doing it myself, plus I know I have someone who represents me and has contact information not available to the average passenger and can often get problems solved quick and easy so I don't have to worry about it. But hey, if you like working on your car, why hire a mechanic even if they charge the exact same price as it would cost you to do it yourself?
As for this request, during high travel times, quads and triples are the first to get booked since that's what families want. So unless you get really lucky, as others have said, chances of finding two cabins for 5 people are going to be slim and none, especially at this late date.
There are some last minute options available, but you'll have to open your requirements to other cruise lines, ships, and/or dates.