A man in the middle attack can be a scary situation. Now, to be clear, this is only happening with on your phones? There are no computers or other devices connected to the network?
Are you certain that you're connecting to your own network? A man in the middle attack may occur when a hacker sets up a spoofed network that looks like a legitimate network that you normally connect to. I would double check to make sure you don't see that your WiFi network has been duplicated.
Another common place to have this happen is public WiFi networks. Do you use public WiFi? I personally would recommend that you never connect to a public WiFi network as they're not secure. If you must use public WiFi, then you should protect yourself by encrypting your connection via a VPN.
You can find out more about these attacks here: Defending Yourself from a Man in the Middle Attack (kaspersky.com)