There's only a limited amount of rust in each car

Welded the pieces back together, cleaned surroundings and painted the area. Good enough considering it won't be visible in complete car.

Then the next rusted spot. This one is the worst area I've found in this car. Had to ponder the situation for a while where to start and how.

I removed the driver's door and ripped off patches that were poorly welded to hide the rusting pillar. I think I'll fix the lower section first. Wondering should I remove the windshield before I even try to fix the upper area.