By looking at those pictures I say those doors are junk. Barely any metal left, especially on the front doors. And since there is no way to get to what is left from inside, you wont be able to stop it from spreading further. Applying any coats will most likely accelerate the rusting. Save your time and money. Clean what you can and apply any oil non drying product to slow it down.

 

Ive seen videos on applying oils to the inside of the door bottoms to slow/stop the rusting. Luckily this is all on the inner side of the door bottoms, not the outside skin and still really solid as I chisled on them with a screw driver to get the "Barnacles" off, so they should have quite a bit of life left in them, Ive seen several decent HHRs being sold as junk/parts cars for $600 and less that only have blown motors or trans, bodies are excellent so I may snag one and strip it down for parts and scrap the rest.