Multiple transmitters and problem with ref
You want to send data from 3 (or 4?) different Arduino transmitters to one Arduino receiver and you want to be able to distinguish the packets sent by each transmitter as they are received. The most straightforward way is to create a struct for your data and attach a unique header and trailer that can be used to identify the sender.

typedef struct {
  uint8_t header = 0x01;
  int temp1;
  uint8_t trailer = 0x10;
} PACKET;


Something like this should be present in each transmitter but with unique header and trailer for each one. Then the receiver should have the header and trailer bytes for all the transmitters and, whenever it receives data, it checks the first received byte against the list of header bytes to know who sent the data before it continues. Finally, it checks the last byte to know if it's the correct trailer byte for the assumed sender and also as an additional (but perhaps unnecessary) layer of error detection to know if the received packet is a complete valid one.