If it's anything like our census Melody, every household would get their own. They're compulsory here in Australia as well every 5 (I think) years.

As you have 2 households in your apartment block, check to see if the other family received the census forms, and if there's only one form, I'd suggest that you try to find out if everyone needs to fill one out, or if it's a random selection of residents. Maybe you were both supposed to get one, but only one arrived.

I'd say that apartment one would be the apartment on the ground floor; apartment 2 on the top.