Do I need to pay royalties fee for this?

Ah OK.

In that case the move would be to contact Epic’s licensing department as to what would be considered a unique requirement that you probably would not get a response to in an open forum. Making licensing policy on the fly = bad idea.

Epic has a brand new licensing office just to handle such situations.

You can contact the licensing manager for North America, Jason Mangold, at Jason.Mangold<at>epicgames.com