I was wondering if it's possible to upload fortnite into unreal engine?

Is it possible to add my own stuff into fortnite and play in it, even though i wont play with online people is it possible for me to just upload the fortnite files into unreal engine and mess around with the fortnite files?

No, because 1. You can’t open cooked assets in editor 2. it’s probably against Fortnite EULA