Connecting industrial devices to OPC server while keeping segregation

Solution 1:

By the way, 192.169.0.122/.123 are no private IP addresses. You should never use public addresses that you're not authorized to. Check out RFC 1918.

There are two basic approaches:

1. You configure a separate network (p2p, switch, VLAN) for each machine and connect one server NIC to each network (but both within the 192.169.0.120/21 subnet or larger - which subnet mask to the machines use?). Then you use explicit entries in the server's routing table with low metrics to control which destination goes out of which interface. Note that host configurations are explicitly off-topic here.
2. You create a shared network (VLAN) but use a switch with a private VLAN aka port isolation option to inhibit traffic between the machines' ports, just permitting traffic between the server and each machine.

I'd prefer #2 as a neater solution.