I would guess that a system with just 5 POTS lines isn’t using ARS.

Assuming that the 5 lines are in one trunk group, I would start by splitting them into two groups. Line 1-4 in one group and line 5 in the second. Make the ring in destination the same for both, but don’t use the second group for outgoing. That will keep one line always available for an incoming call.

From there, build the Facility Groups to use the local lines first, then the remote node. Change the outbound extension from the trunk group to ARS. If the sites have different local calling areas, expect dialing issues.