Did you see the other link? It doesn't use any libraries and it clearly mentions pins D13 and D8, but same result.
Different library. Different setup. You can't take the wiring from one setup and program and use it directly with another. This stuff rarely/doesn't work that way.
Do you have a posted example of how to wire those 4 units and the code for them?
You don't need (specific RS-485) code for for that setup. That's the point.
Actually all I wanted for starting is to have one unit as the sender and one as the receiver and try to send text from one to the other and see how it works, then I can expand from there.
You say want to start simple, but are starting complex. So let's back up and do what you say.
Step 1: Put aside the RS-485 modules. Can you
have one unit as the sender and one as the receiver and try to send text from one to the other
and get that to work? Just connect the Tx/Rx pins you intended to use with the RS-485 modules, together and connect the grounds. When you can get data sent between them, then go to step 2. You need to actually do this, not just say you can.
Step 2: Replace one TX/RX line with a pair of modules, connecting DE/RE to 5V or ground. This replaces one of the wires between the modules, with a RS-485 differential pair. There is not code change required. If step one works and this step doesn't then there is a wiring problem.
Step 3: Repeat step 2 for the other RX/TX wire. There is not code change required. If step two works and this step doesn't then there is a wiring problem.
Step 4: Now that you know you have the wiring correct, connect the DE/RE wires to the Arduinos (this will be two wires to one arduino pin). Now you can work to get the code for the DE/RE pins working.
Step 5: With step 4 working, remove one pair of the modules which will put the setup in final form. There is no code change required to get this working. If step four works and this step doesn't then there is a wiring problem.