We decided to hand wash (step on in tub) the covers. It took 3 washes and 3 rinses but they feel much cleaner!
We also found out that by steaming the foam cushions with a clothes steamer you can "repair" the condensed foam. Pretty excited about this one as we can salvage the original foam that was in decent shape for a few more years!
The foam on the left has been steamed and the foam on the right has not.
Thanks everyone for your suggestions!