I am thinking about a new Doorbell system to replace the original one. the system is a Door-Station on the Yard, a Door-Station on the House-Door, and a Phone in each of the three Appartments. i wanted to replace the stations with a Arduino each. they have to communicate via 2 wires. is this possible? and if so what are the requirements? (wiring) the planned setting is: arduino 1 and 2: 3 buttons(to determine appartment) Speaker Microphone, Arduino 3-5 Speaker Microphone button (to open Door)
is this possible?
The Arduino will be capable of performing its role. Whether you are capable of installing the hardware and writing the code and making the proper connections is not for us to say.
and if so what are the requirements?
You've got that backwards. You need to tell us the requirements.
What are the wires for? That will define where you connect them and how you use them.
What are the speakers and microphone for? The Arduino is not fast enough to do digital signal processing, to convert microphone input to digital data, send it somewhere, and convert the digital data back to audio data to pass to the speaker. On the other hand, that really doesn't need ANY processing. So, you won't actually be connecting either of them to the Arduino.