Hi Leslie,
These songs are not royalty free, but they are not registered for Content ID, meaning platforms like YouTube and Twitch cannot detect their usage. I chose not to, so to avoid that kind of situation.
If you ever have any issues, as the developer, you of course have the license that you get when you buy the pack from here, to prove that you have the rights to use that specific audio track. For streamers, I believe that when they show the game footage or gameplay the copyright will fall into the "Fair Use" law, since it's beneficial for everyone. But as I said, having not registered the tracks for content ID the algorithm should not detect and start annoying complaints automatically (and no complaints will be manually created by me of course :) ).
I hope this answers your question!