Hello Greets.
I am having the same problem re: <INCLUDE> files ... apparently, UEStudio cannot find them if they are in a separate folder from the source files.
You might be able to make this work by looking at another message of mine under the "Projects / Solutions" header (not sure if that is the exact name) ... you will probably need to add these via an additional key such as "Additional Include Directories". At least I have been able to tell the compiler where to look for them, unfortunately, the UEStudio IDE doesn't know yet...
Let us know if you get stuck ...