If 2 devices (slaves) operate at the same baud, voltage. Is it not possibble for the Master (tx) to transmit to multiple Slave (rx) if each slave expects a different set of command sets. Then theorectically only one slave will understand certain commands as the other will treat as garbage.
Yes, that should be no problem.
It is then understandable that a XOR gate from the Slaves (tx) will negate if neither are transmitting or in some cases when both transmit when powered on (ok...ready).
There are two problems with connecting two slaves' TX pins to a single master RX pin.
An electrical problem arises because both slaves will hold the RX high when it is idle and that prevents the other slave from pulling the line low to send data. The Master also requires the line to be high when idle, That problem can be resolved by using an external resistor (perhaps 4700 ohms) to pull the Master RX high and putting a diode on each of the slave Rx lines so a slave can pull the master low but cannot drive it high.
The logical problem is how to ensure that only one slave trys to transmit at any one time. That could be solved if the master sends a special message to a slave inviting it to transmit.
Serial Input Basics