The best and the only 100% solution is to use separate physical infrastructure … both ethernet cables and (if needed) WiFi access points using uncorrelated channels. I guess that using common router should be fine if IP cameras have to be accessible from internet (or the rest of LAN), but be sure that router’s CPU is capable enough to handle all tasks “with ease”.
If that’s not possible, you can try to implement some QoS mechanism on the shared part of network. This might not be as effective as the first solution.