Hello Arhum,
Yes, it is possible to connect two ADALM-pluto as transmitters in a single simulink model, to do that, download 'Communications Toolbox Support Package for Analog Devices ADALM-Pluto Radio' support pacakge which will be available in MATLAB Add-ons.
In simulink, search for ADALM-Pluto transmitter block and set their properties accoringly, especially to which usb port the device is connected.
Refer to below documentation link for more details:
Regards
Naren