After many years, I am coming back to get 3 RFID readers to work together again. Completely forgot how I did it , I started with Software serial. I couldn’t get two software serial ports to work. After reading the notes I left for myself in this post (https://www.ivadream.com/kyle/red/?p=4344). I found out from myself that in order to get 3 RFID readers working on 1 Arduino, I had to use 1 hardware serial, 1 software serial, and 1 altsoftware serial. It worked like charm!