https://docs.unrealengine/latest/INT/Resources/SampleGames/ShooterGame/index.html
As this is a free sample, anyone can have a look at it.
BTW. awesome sample.
What’s the legal small print with the samples?
Can I use resources from the Learning Sample Projects, like sounds, textures, models in my own commercial games projects?
Yes, you are allowed to use those assets for your own games 
https://answers.unrealengine/questions/21462/can-we-use-stuff-from-samples-like-rocks-and-trees.html
https://answers.unrealengine/questions/26453/unreal-engine-stuff.html
oh wow, that’s cool
So just to be right here i can download the cave demo game and use the cave walls in my own game? and if i sell it later on i give the 5% of the sells yeah? i just want to be 100% sure 
Yep, you are allowed to use all the free content on the marketplace for your commercial and non-commercial games
"UE4 is available for $19 per user per month, with a 5% royalty on gross revenue after the first $3,000 per game per calendar quarter from commercial products. "
Thank you for your help!