Yes you can. The intercoms have four different channels they can be set to as well as a “paging” channel. Each intercom is capable of communicating with only other intercoms which are on the same channel as well as communicating on the “paging” channel regardless of the private channel the intercom is set to.
The CHNLS2 systems has a “monitor” mode which allows one intercom to be “locked” open and the other intercom to be locked into listening mode. This works than as an excellent long rang portable baby monitor.