Point to Multipoint Connection to Multiple UAVs with single GCS

Hi.
I want to connect multiple UAVs those have RFD900x onboard to use as telemetry link.
Is there a way to connect these UAVs using a single telemetry modem (RFD900x) on the GCS using MAVProxy?
I am able to build the PtMP link using modems but I have a MAVProxy issue.
I did some experiments with MAVProxy and SITL using point to multipoint configuration of the modems.
First I started two SITLs using
```
arducopter -S -I0 --model copter --defaults /home/m/ardupilot/copter1.parm
arducopter -S -I1 --model copter --defaults /home/m/ardupilot/copter2.parm
```
Parameter files only holds the followings (individually):
```
SYSID_THISMAV 1.000000
SYSID_THISMAV 2.000000
```
Then i am connecting these SITLs using MAVProxy:
```
mavproxy.py --master tcp:127.0.0.1:5760 --out=/dev/ttyUSB1,57600
mavproxy.py --master tcp:127.0.0.1:5770 --out=/dev/ttyUSB2,57600
```
Where “/dev/ttyUSB1” is for SITL 1 and “/dev/ttyUSB2” is for SITL 2 individually.
And also the modem connected as “/dev/ttyUSB0” is P (center) of PtMP configuration.
And “/dev/ttyUSB1” and “/dev/ttyUSB2” are the MP (end nodes) of PtMP configuration.
Now I am running this command to open the center node:
`mavproxy.py --master=/dev/ttyUSB0,57600 --out udp:127.0.0.1:14550`
When I fire up above command I see some movement on the console of the individual MAVProxy terminals of the SITLs.
But when I want to separate this communication via the following individual terminal commands:
```
mavproxy.py --master=127.0.0.1:14550 --target-system=1
mavproxy.py --master=127.0.0.1:14550 --target-system=2
```
Only the second one stays alive and the other one breaks communication.
For example when i first do mavproxy.py --master=127.0.0.1:14550 --target-system=1, then mavproxy.py --master=127.0.0.1:14550 --target-system=2 on sepearate terminals, I am able to communicate with System 2 but not System 1.
But when i first do mavproxy.py --master=127.0.0.1:14550 --target-system=2, then mavproxy.py --master=127.0.0.1:14550 --target-system=1 on sepearate terminals, I am able to communicate with System 1 but not System 2.
How can I solve this issue?
Thanks…

Reproduce the two SITLs and MAVProxy commands shown in the report, focusing on the shared UDP endpoint and separate --target-system sessions. Trace MAVProxy's handling of target selection and multiplexed MAVLink traffic; done means both system 1 and system 2 remain reachable concurrently through the single telemetry modem.

Written by the indexing model from the issue text.