I Figured It Out!!!!!
After days and days of googling my problem, I finally tried something that worked, and it was all too simple!
This is what I ended up putting in the body tag of my gallery page that has the iFrames on it:
Where "iFrameName" is the name of the iFrame I am targeting, and "iFrameContent.html" is the .html file I want to initially open in the iFrame when the gallery page is first opened. If you have multiple iFrames you don't want empty when the page opens, the code would look like this:
<body onload="iFrameName1.location='iFrameContent1.html', iFrameName2.location='iFrameContent2.html'">
In my case, I need the gallery page to open with different things showing in the iFrames, depending on which link took you to the gallery page. So...what I will do is create multiple gallery "start" pages and change the <body onload=...> tag.
I hope this helps someone. I found a lot of people with the same problem and no responses, so here you go!
You just need to make sure that the .html file you want to open in the iFrame has the correct path according to whatever page your iFrames are on.