Is it possible to use instances of the TX/RX of a Uno board, i have a Nextion HMI & Maestro servo controller that needs to use both inputs/outputs at once
No.
You can use software serial (or the alternatives like altsoftserial or NeoSWSerial). Also be aware that equipment connected to RX/TX can (most likely will) interfere with uploads and your ability to use serial monitor for debugging.