An object can either have one image like tiledbg or animations like Sprite defined with the pf_texture or pf_animations flags. Not sure if you can have it load more than one texture by default though.
As far as drawing goes you can draw the two textures any way you'd like at runtime. The edittime is more limited though. You'll have to look at the Sprite plugin to see how different animation frames are used for drawing in the editor. Also it doesn't look like you can control the blend modes for the editor from the sdk, but maybe I haven't looked well enough.