I have a couple of fonts I want to use on my design inside Avery online, but I don't know how to get them into the font option list. Is this even possible?
You can't add your custom fonts to an online application. The fonts are on the server and the only way to add them to the application's Fonts list is through the developer. He is the only one capable of accessing the server's folders to store the fonts then replace the necessary code in the application to recognize them. You will have to contact him in order to add a font.