Just a heads up if you haven't caught it yet, but the tire in the
front left image has a visible tread splice if not a torn splice. RT-660s are known to do this quite badly—just search for RT-660 splice on your search engine of choice.
This article from Tire Rack talks a little about how to rotate them to avoid it getting worse, but ultimately recommends tires with torn splices be removed from service. I don't know if I'd go that far, but if you haven't already (and if it's possible) I'd put that tire in on the rear. Given the RT-660s propensity for developing exposed splices, I'd continue to keep an eye all 4.