If you want to use the BatchPreprocessing script you need at least bias and dark frames. In fact, the main reason for the existance of the BatchPreprocessing script is to do image calibration, so unless you have bias, dark, and flat frames there isn't too much point to using the script.
So, you'll have to do a manual debayer operation (BatchDeBayer script), followed by StarAlignment (under ImageRegistration), and then ImageIntegration. For a quick practice run with three files you can probably just use the defaults for each process and it should take only a few minutes to perform the entire set of operations.