adressing for point to multipoint network, no adress masks?

We have been using the Xtend radios for a few years now and have been very happy with them. Our product is now migrating to Xbee-pro 868mhz so that it can be used in Europe.

I have read the user guide of the XBee-pro 868 modules but I am having a very hard time figuring out the adressing scheme for a point to multipoint network. I see that adress masks are not used and the source adress cannot be changed.

So my question is the following:

-how to set the adress for the base station so that it can talk to all the remotes, and the adresses of the remotes so that they can all talk to the base, but not to other remotes (a “star” network)?

This could probably be done by polling and discovering the source adresses of all the radios in the network, but this is impractical because I do not know ahead of time how many remotes are in the network, and remotes can be added or removed at any time, while the network is in operation.

Thanks you for your input.