Pass traffic from one network interface to another

I have a project where I have 4x RPiZ plugged into a single RPi4. The RPiZs appear as Ethernet over USB devices as network interfaces ethpi1, ethpi2, ethpi3, and ethpi4 with IP addresses 10.0.11.2, 10.0.12.2, 10.0.13.2, and 10.0.14.2 respectively. The RPi4 is on a network I have access to with a known, but not controlled, IP address like 192.168.0.2 or something. I won't have physical access to the device once it is set up. All 5x RPi's have a FTP (proftpd) server, a HTTP (lighttpd) server, and SSH enabled. I am trying to figure out how to access these servers on the RPiZ's without first SSHing into the RPi4. This involves multiple related questions. If I have a computer on the same ethernet network as the RPi4, how do I direct traffic to/from the RPiZ's?