Question / Help Not possible to use two external cameras via USB

[Krutomluv]

I can't connect two cameras via USB - I ve tried to attach two iPhones but only one works. Is there any solution? Thank you.

 

[Tangential]

I have successfully used 2 USB3 encoders on my 2015 15" MBP at the same time (although I prefer to use 1 USB and 1 Thunderbolt.) What type of mac are you attaching them to? Are they both on the same hub?