House Paper

My wife and I bought our condo about 6 months ago. We have just got around to thinking about switching her house paper, and getting a house paper for me. As i understand it, if you have a house paper saying that the property has been your primary residence for the last 2 (or 3?) years; when you sell it you pay alot less tax.

It gets interesting because the condo is 2 units, which have been made into 1. We bought it when it was already 1 unit, but it has 2 seperate deeds, one for each unit.

So i figured no problem, my wife will get a house paper saying she lives in unit A, and i get a house paper saying i live in unit B. Thus when we sell the condo we wont be paying taxes as if we never lived there.

However when my wife called the District Office about the house paper they said foreigners cannot have a house paper saying they owner a condo, but i could only be on my wifes paper as a resident of her condo, is this correct?

Ideas, suggestions?