Arlene, the mold seeds/spores are always in the air. They need someplace to sit and water to grow. The moisture that's in the air or your floors or walls gives that to them. If you get rid of the moisture/humidity, you can get rid of the mold. Bleach will kill the mold for a while, but since the spores are in the air, all they need is water to start growing again.
It does sound like you have a big problem and you might be able to get some help with it. In some parts of the country (USA), the government will help with mold abatement if it's in walls and in basements heavily. I'm sure not qualified to determine, but you may want to check this out. I think that HUD handles the program. Mold can be dangerous for some people to be around, particularly kids and people with asthma.