Phones without a "server/PBX"

[kermitxyz]

I am maintaining a system with four IP phones. There are on a LAN but have no SIP service (they are just used as an internal system) and dial each other via IP address. Outgoing calls are made via a bluetooth mobile connection.

1. Can I assign each phone a name so that name shows on the receiving phone when a call is received (i.e. “bedroom” rather than “192.168.10.54”) ?

2. Is it possible to transfer calls in this setup (i.e. phone A makes an outgoing calls via bluetooth connection to a mobile – can phone A transfer the call to phone B) ?

3. Can I have a shared contact directory for all phones?

If in either case the answer is no, is there a simple and ideally opensource PBX I could internally on a small server to do these?

Thanks!