To share using a dial up.. you need one computer always ON.. then use a software such as Wingate, Winproxy or sygate.... this way anyone just turn on their pc and it will dial automatically... (don't forget to disconnect after using... While this line is in use .. you may not be able to use it to call someone... unless you have another software that have a call waiting or something...

Please note that you don't need to connect a phone line to all pc... just a network cable and a router/switch or maybe just a Hub. And there is no wireless in your system... because you don't have an Access Point.

Now, after you get a dsl line (its only need one phone line.. and may or may not came with a Modem) you will need a an Access Point with or without router plus a Wifi adaptor for each pc you have.

The connection, more or less will be like:
Adsl Modem ==> Access Point with or without router ...... then all pc connected through wireless.