I'd find a front loading washing machine somewhere, and run what ever will fit through at least 1-2 cold water washes, without any soap or anything. That should remove the bulk of the cat urine from them. Whatever doesn't fit in the washer can be cold water rinsed with a hose outside, or in the bath tub. With that amount of urine, you HAVE to rinse it out first.
Then I would either soak the cushions for 8 hours, or overnight in oxygen bleach in the bath tub, or saturate them with Nature's Miracle.
The cushions may not be the same fluffiness when you are done, but they will be clean.
And definitely get the cats in for a check up ASAP. In the meantime, locking them up when they can not be supervised, in a room where they can't get at anything fabric or paper will reduce the chances of this happening again.
Also, if you don't have 3 litter boxes, make sure you do from this point forward. 1 box per cat, plus 1 is the rule of thumb.
He who can no longer pause to wonder and stand rapt in awe is as good as dead; his eyes are closed. ~Albert Einstein