If I have an ad group containing one text ad and one image ad - can both ads show at the same time on a site if the "display site" has both text and image ads?
If not, perhaps I can make this happen by separating the text ad and the image ad into separate adgroups (with same keywords)?
The answer is "no" for both ideas, I'm afraid. For any given keyword (Search) or site (Display) only one of your ads will trigger at any time,
Google has very strict policies against even attempting to do this - known as "double serving" - see below: