Yes you can freeze soup in plastic containers and they will be just fine.
Even if the plastic container is not labeled freezer safe you can still freeze the soup in plastic containers.
I use old butter tubs and other plastic containers to freeze soups and other foods in and they have always been just fine.
You can also put soup in plastic bags such as Ziploc bags or other freezer safe bags and then freeze the soup that way as well.
Just make sure the soup is cooled down before you put them in the bags.
When frozen the soup will last for up to a year but it's best to eat the soup within 6 months so it is at it's freshest.