Cubase 12 midi guitar with another controler problem

Hi
Im having problem understanding ,how to use two inputs(lets say midi guitar and abreath controler).with cubase12

When i chose on the vst input midi guitar,its works great,but when i chose all midi inputs, its dosent recognize midi guitar but can recognize my other midi controlers(keybords,drums)
What ,am i missinig?
Thanks
Tomy