Is it possible that I have caused a DoS to my son's tablets [migrated]

I have three Internet connections at home, they are not connected to each other in any possible way, they are from three different ISPs

• FTTC #1 , the white modem and the black and white router


• FTTC #2 , the BT black modem/router


• EE 4G , the white square modem/router

My two years old son uses two iPads at the same time, one is connected to FTTC #1 and the second is connected to EE 4G. Rest of the house uses FTTC #2. Obviously we all use WiFi.

This morning I was downloading a huge amount of files from an FTP server using my laptop that is connected to FTTC #2 over WiFi. Both iPads could not connect to their networks. at first I thought something is wrong but once I stopped downloading both iPad went back online. To be 100% sure I resumed the download and all the sudden both iPads had problems authenticating to their networks, one of them kept trying to connect while the other kept asking for password repeatedly.

I always assumed air was a huge pipe that you can never block and cause congestion?!