The only Portuguese double sided Homelands card we've seen so far could not have been created by printing a full sheet upside down on another sheet. It could have been created using the same process described above for the German Uncommons as a Row #1 / Row #5 combination. Assuming that this is what happened, Here are the card combinations that would have been printed. (All in Portuguese)
The Axis is row #3. These 5 cards were in the middle causing them to be printed with themselves on the back.
Dry Spell
Torture
Shrink
Memory Lapse
Mesa Falcon
Row #2 was printed with Row #4 upside down on the back.
Joven / Anaba Shaman
Abbey Matron / Hungry Mist
Serra Paladin / Clockwork Steed
Ambush Party / Anaba Bodyguard
Serra Bestiary / Labyrinth Minotaur
Row #1 was printed with Row #5 upside down on the back.
Carapace / Trade Caravan
Cemetery Gate / Sengir Bats
Dark Maze / Reef Pirates
Carapace / Torture
Cemetery Gate / Aliban's Tower (only Portuguese card we've seen so far)
Here is a picture of the top left quadrant of a Homelands Common sheet. I cropped off the rest of the sheet to help you visualize how these cards were printed. Sorry for the poor picture quality.

As far as quantity, all we know is that we have multiples of the German Uncommons and only one Portuguese Common. Maybe the "less interesting" Commons were destroyed, or maybe less were actually printed, or maybe they are yet to be discovered?
Tav