Do I need to kill Railroaders when playing for Institute? How to avoid killing them?

I play for Institute and there is a quest "End of the Line" where the Institute wants me to kill Railroaders.

There is a video where someone avoids killing them, but there is a lot of information missing how to reproduce it, I am unable to do it:

The quest is also not well documented on Fallout wiki: http://fallout.wikia.com/wiki/End_of_the_Line

So is it possible to avoid killing the Railroaders and what are the steps to do it?

If you want to complete the Institute storyline in the unmodded version of Fallout 4, you must turn on the Railroad. Once you get End of the Line, the quest will only resolve if you take one of two actions:

• Kill Desdemona. This makes the Railroad hostile toward you.
• Warn Desdemona. This keeps the Railroad friendly and allows you to progress through their quests, up through Rockets Red Glare. At this point, you'll receive the quest The Nuclear Option from the Railroad, where they ask you to attack the Institute. This forces you to choose which group to attack to progress further in the story.