The MCP39F501 should use a full duplex RS485 transceiver (two RS485 links). The RE (Receiver output Enable) and DE (Driver output Enable) pins should not be tied together. The RE of the transceiver should always be enabled and the DE should be tied to the DIR pin.
In this case, all the device should receive is the command from the master (PC). However, only the node that matches the address sent should enable its driver and allow it to send data to the master (PC). The RX RS485 link should be connected in parallel with the other RX485 link and connected to the driver of RS485 of the master. The driver RS485 link should also be connected in parallel with the other driver RS485 and connected to the RX of RS485 of the driver. This should eliminate bus collisions.