They're not from other games, they're remixes. Also, trees might be awkward to walk by, but it's possible.
Viewing post in Tenebris, Erroris jam comments
Yes, they're remixes of songs from other games. Using them is still frowned upon in game jams.
At the very least, please credit the website you got them from and the person who made the mix. It's part of their terms of use.