Hi,
iMX8MQ supports 2 MIPI CSI-2 port, so you can connect 2 cameras.
No.3 camera should be connected to USB port.
so you cameras will be : 2 of them should be MIPI CSI-2 interface, 1 of them is USB interface.
Hope the information is helpful to you.
Have a nice day!
B.R
weidong