In some instances it has been found that using multiple of the same cameras Studio will not display source from more than 1 despite detecting all of the cameras. To resolve this issue you should access your camera's settings and configure the network hostname to be unique for all the cameras.
IE: if you had a configuration that showed 3 cameras in studio all called "NDICam (IP Address) , NDICam (Default) , NDICam (Default)" you should change the hostnames to "NDICam1 , NDICam2 , NDICam3" as Studio ignores the name within the ( ).