You can bake two casseroles at once even if their recipes call for different oven temperatures, but first consider whether each dish needs gentle heating or a crisp, browned top. A shared temperature may work for dishes that only need reheating; otherwise, stagger their baking times and check each one for doneness.
Essential Concepts
Share a temperature when the dishes allow it; stagger them when they do not.
Related posts: /thanksgiving-oven-planning/ and /oven-rack-placement/