If your master keyboard cannot control several instrument instances standalone (deficient USB MIDI driver), a very simple way is to download LOOPMIDI by Tobias Erichsen and Bome’s Mouse Keyboard by Florian Bömers. Include loopmidi in windows startup programs, and launch bome’s mouse keyboard. Indicate your master keyboard in MIDI in from B-M-K and loopmidi port for MIDI out from B-M-K. In the vst instances, select “loopmidi port” as the input port.
HI @Kléroterrien and welcome to The Sound Explorers Forum.
Thanks for the heads-up! I think some people might find that rather useful!