Ana - I am not making myself clear - sorry. You pick/highlight the photos you want on the page
before you drag them. Or if using Upload File then you select/highlight as many as you like when you browse/select -
before you upload. Just like I did in this first screen shot. Do you see that I have highlighted four files for uploading.
Then you can drag all of these photos together, just as I can do in the wiki. What you see highlighted here are four photos that I selected in order to drag them all into the same page at once. I am guessing you do not know how to select multiple files from the same folder (as I did here) - could that be the problem?
Then I drag all of those into the wiki bar like this.
And then I can click them, upload them,
and insert them all at once as a Gallery - like this. All of this with only three clicks of the mouse. Drag, upload, insert.

Or I can insert them where I want. No more need to copy and paste code in the wiki, it is done automatically. The only thing necessary is to add the parameters for size, comments, or position as desired
.