Seeing you need synchronization only on a frame basis, this should be rather straightforward: nothing in your microcontroller needed to initiate the camera giving images takes in the order of 1/60 s.
So, you'd just write firmware that takes some start signal (for example, simply a GPIO input going high) and tells the camera via I²C to start sending data. If you share the same trigger with all microcontrollers, this should be rather straightforward, and the timing insecurity, especially if the triggering happens in an interrupt, should be far below 1/FPS.
Regarding how to connect 8 of these cameras to one application processor: well, tough one, because this is a lot of data.
The 100 Mb/s ethernet integrated in your MCU is not fast enough for uncompressed full HD at 30 FPS (30 F/s * 1092*1080 px * 12 bit/px is about 283 Mb/s). So, that can't work.
The only other fast interface is the USB2 High-Speed interface, which, with 480 Mb/s is nominally fast enough for 12 bit per pixel, but you'll find that it's not trivial to write USB firmware fast enough. So, you'll need to write a firmware that deals with camera data, and makes sure it is DMA'ed into the USB peripheral buffer. Of course, you'll have to implement the USB stack. NXP does have an app note on how to implement a USB Webcam style device with your MCU, but it does 640x480 at 20 fps, not six times that resolution at 1.5 times that frame rate.
Then, you will have to aggregate all that data over USB at your central processor. I doubt you've made a good choice there – you will need, bandwidth-wise, a high-speed USB controller per camera, and your central processor doesn't have 8 of these.
So, all in all: I think both your MCU and your central controller are the wrong tools here.
Realistically, you'll want an FPGA on which you can instantiate 8 MIPI CSI interfaces, and then have one link to your central controller CPU; probably via multiple PCIe lanes. That'd solve the USB bottleneck, but it does not solve the fact that this is much data, and it's very questionable your cute little quad-a72 core processor (since your workload is fully identical 8 times, the littleBig little-cores cores don't help that much) will be able to deal with 8 camera streams. Don't forget that having one or two video processing chains does not make dealing with 8 video streams simple, by any means.
