you can run lightningd --help and get a list of arguments you can use to start lightning from the output there ist:

--lightning-dir=<dir>                Set working directory. All other files are
                                     relative to this
                                      (default: "/home/user/.lightning")

this means that you can set your own lightning-dir by calling lightningd --lightning-dir=/some/path/to/some/directory

now you can either put all the config values as additional arguments to your call or you put a config file into /some/path/to/some/directory/ which sets everything. the default is to call it config but you can also use the command line argument --conf=/path/to/some/conffile from lightningd to set a different one in a different location.

One thing you need to remember that both lightning nodes need to run on different tcp/ip ports. you do this by setting the port in your accounce addr in the config file announce-addr=IP-ADDR:PORT you need to replacei IP-ADDR with your address and the port with the port.

obviously when interacting with each of the nodes you need to tell lightning-cli which one. again the --help command helps (:

lightning-cli --help
Usage: lightning-cli <command> [<params>...]
--lightning-dir=<dir>  Set working directory. All other files are relative to this (default: "/home/user/.lightning")
...

this means you can for example do lightning-cli --lightning-dir=/some/path/to/somedir/ getinfo