Does living next to an electrified railway cause WiFi outages?
The answer is "Maybe". If you look at trains moving along such lines you often see sparking. This is going to cause RF interference. Additionally, the length of the power line itself might act as an antenna radiating the interference.

They need to do some experiments. Record the exact timing of the outages and see whether it correlates with trains. Also, have an AM radio on and see whether they can hear interference at the same time as wifi outages.

The key thing is to find out whether there is a correlation with something visible happening. If there is, contact the owners of the railways. Otherwise, it may well be interference from elsewhere.