Good morning.
I believe you are trying to say you want to install an SIP server either centrally or per house. In either case you can simply go for 3CX IPPBX system, which free of cost. I can install it on your Windows server box and can configure it to receive calls from other SIP clients. You can assign extensions up to 5 digits. The system will be able to makes and receive calls from anywhere in the world if you give it a static public IP (the actual box can reside within a LAN with port forwarding configured in the router).
Later you can configure it to attach to PSTN lines & other SIP servers, known as trunks.
If this is the case, let me know & I can install the 3CX Phone System on your boxes.
- Joy