Update: I found something about Pineapple and Prickly Pear wine.
Apparently Pineapples do not have enough natural sugars in them to support fermentation. The addition of Inverted Sugar is necessary. Out of a 5 gallon batch only a half gallon would be pineapple juice, which would make it just flavored water. It may be better to flavor a white grape wine with pineapple juice to get away from using Inverted Sugar. Acid Content is also a problem, which is probably why so little juice is used to make the wine.
As for Prickly Pears....
It's almost the same story as Pineapple except alot of regular white sugar needs to be added over time, not inverted sugar. Out of 5 gallons, only 2 gallons is Prickly Pear Juice.
You may want to make one gallon at a time until you find something that works. Since I mostly make wine from fresh fruits or berrys that are in season, I usually only make wine in one gallon glass jugs, unless a whole bunch of berrys come in at the same time, which normally doesn't happen.
I used a 5 gallon carboy once last year for Blackberry, the rest was made in one gallon jugs. (I have 30+ of them, and always lookin for more.)