ANSI can convert to TCHAR by simply putting it in an FString. Internally it has a TCHAR array, and can be accessed as such with *.
ANSICHAR ANSIStr[8];
FString MyNewStr(ANSI_TO_TCHAR(ANSIStr));
Then converted to UTF8 via
ANSICHAR* MyUTF8 = TCHAR_TO_UTF8(*MyNewStr);
NOTE: This pointer must not be kept for long, you need to copy the data out as the memory will be release when the code goes out of scope.