Quiz

I believe the default behavior is to import one at a time.

If you know what you are doing, you might be able to combine multiple XML files with a text editor. However, the time it would take to do this would probably not save you any overall time importing the individual files.

The Moosh command-line tool supports importing Moodle Question XML files directly into a quiz (see https://moosh-online.com/commands/#question-import) or a question bank category (cf. https://moosh-online.com/commands/#questionbank-import). However, you must specify the quiz ID or the question bank category ID, which might be tricky. You also need command-line access to the Moodle server for this approach. A better solution would be to write an XSLT script to combine multiple files into one, and then import the final output into a course question bank, see https://stackoverflow.com/questions/9693431/combine-multiple-xml-urls-into-one-xml-file-with-php-xslt for a starting point.