As you said, you have four different networks:
192.168.123.0
192.168.123.64
192.168.123.128
192.168.123.192
You need to put each of those as a separate network into your calculator. Your calculator will only work on one network at a time, and you have four networks.
If you enter 192.168.123.128192 as the network with a mask of 255.255.255.192, you should get 192.168.123.193 - 192.168.123.254 as host address range.