Reminder: you cannot win a debate with a gamergater, alt-righter, or any other internet troll.
Want to know why? For starters, there's no debate to be won. They aren't there to discuss ideas and opinions. They are there to put on a show.
You are operating in the realm of True and False, of facts vs. fiction. But they aren't operating in that realm at all. They are operating in the realm of memes, circuses, and bullshit. Whether something is true or not is irrelevant. Whether it creates the right reaction is what matters, to them.
The best you can do is shut down the conversation: delete the posts, ban them, ignore them, whatever. Deny them their audience and platform. Don't give them anyone to entertain, perform for, or incite.
If you want to help them (and please do), handle it personally. Talk to them without an audience. Then you may able to reason with them.