Can anyone advise if it is at all possible to just have 2 cisco sip phones in my house as sort of an intercom system? I’m not wanting to dial out at all just other extensions on my home network.
With Asterisk yes.
However, with suitable IP phones, you do not need a PABX for that application. I don’t know whether that is possible for Cisco’s, although I would note that they were designed for corporate use, where there would always be a PABX.