#2, "The program must include source code, and must allow distribution in source code as well as compiled form."

Unreal's license for obtaining the source does not permit you to redistribute in source form, so you can't comply with their license and still fulfil that point.

While it's certainly trivial now for most anyone to obtain that source independently, you can't include that source in your own project while still distributing your own project under any license that the OSD would label as open source.

Your project going to be derivative work from UE4. It's mean Epic of course allow you to share it's source code, but you can't grant any more right to 3rd parties than Epic grated to you.

So no way UE4-based project will be FLOSS or even open source.