Now google sites allows you to upload multiple files and this is how you do it!
Navigate to your google site > navigate to the page where you want to upload the multiple files > do not press edit, just click on the add files button near the bottom of the page ....
Then hold down ctrl and click on all the files you would like to upload ....
Then release the ctrl key > click on "open" ....
And then you are done!
This is the result ....
Enjoy! B x