I haven't seen portable air conditioners larger than 9000 btuh. You would ordinarily need 12000 btuh to cool 1200 square feet. Perhaps with the upstairs units running the portable unit downstairs would make the major occupied area sufficiently comfortable, but this is indefinite.
You might install a split ductless 18000 btuh unit. They are made by several manufacturers and only require a wall unit mounted indoors and a small outdoor unit joined by tubing and the wiring.