How should I apply fertilizer to these Roses?

They need to be pruned. Get some air around them.
My momma, who was a master gardner, put crushed eggshells at the base of her roses.

Just wait for the Japanese beetles to do the pruning for you. I had two knock out rose bushes that were like beacons for those damn beetles. They'd cover them in the hundreds or thousands. I finally got rid of the bushes, and my Japanese beetle issue slowed way down. They're still around every year, but don't to go after anything else like they did those, and the overall number seems to be down considerably.