Two wires coming in off the street is correct.
At the master socket, (to identify this you will see components on it’s pcb – capacitors/diodes etc) a third wire is connected. This wire connects to the same terminal to all exteensions throughout. This wire enables the extensions to ring.
There is a newer type of master socket with a small cover. This easily allows the user to disconnect all extensions so BT can check the line when you report a fault – saves them wasted call outs – they don’t take responsibility for extension cabling problems in the main.
There is a maximum number of extensions you can have on one line. I think it’s 4, can’t remember, but each handset has a REN value (ring equivalent number). Exceed the REN capability of your line and hansets may not ring.
Check the handset ringer is not switched to silent.
Check there are no broken wires to any of your sockets.
Check you haven’t exceeded the REN limit of your line.
If you have broadband, make sure each socket has an ADSL line filter plugged in.