Hi harujoruruko,
the light-version of "roaming" as provided by apples "roaming-network" only works if you have an AirPort as "main wifi station" as far as i know. In your case you don't even have a "roaming-network" as defined by apple.
Even tough you could set-up a "roaming-network" with apple devices, sometimes it might be better to go with a managed wifi (controller + access points) to have a professional wireless network with handover functionalities which do not depend on the client you use.
cheers,
Nuq