Is this a double or a single ferret nation? If its a single it is too small. If it's a double the only way it could work as a cage is if you did something like this:
You could use coroplast and make a tray for the inside like the picture. You can't leave the cage upright with all the ladders and lofts though. Guinea pigs need space to run, not levels as they are not good climbers.
If you use the cage in the way that it's used in the picture it's about 12.5 square feet. If you have 3 sows that get along well they should be fine in that sized cage. If you have boars it could be completely different as boys have a tendency to need more space.