I don't care for knockouts myself as I prefer the fussier hybrid teas to floribundas. They have larger flowers, longer stems for cutting, and while they don't bloom as much, I know which ones to pick to make life easier.
For one thing you have black spot and sooty mold.
The blackspot is a common problem with roses and that is why they need regular pruning to open them up, water deeply only at the base of the plant, and you need to use a fungicide or systemic rose care to keep ahead of the disease and insects.
The sooty mold tells me you have probably aphids, scale or mealy bugs sucking on the leaves. Aphids are the most common.
If you have holes in the leaves, rose beetles or slugs or snails may be the problem there.
Deer also like to nibble.
Roses are heavy feeders and are difficult to raise organically. Pest control and preventive anti fungal sprays are necessary.
To make life easier for yourself:
Select roses that have glossy leaves. they wick off water better and have less issues with fungal diseases like powdery mildew. Black spot is harder to take care of and some varieties are more prone to it than others. You need to do your research and look specifically for resistance to blackspot.
Plant roses so they have good air circulation all around them. Not to close to a wall or other plants. Plant garlic, garlic chives, allyssum, marigolds, under or near roses. It hides the bases and repels some insects from the roses. Four o'clocks or feverfew can be planted nearby, they trap beetles but should be kept away from children and pets. Four o'clocks reseed so you need to take them off if you don't want seedlings everywhere and feverfew is also invasive so I'd keep that in a pot and take off the flower heads.
Roses like a lot of organic matter in the soil but also like to be well drained. Water deeply but infrequently once they are established. For the first two to three weeks after planting you may have to water once or twice a day.
Roses bloom in 6 week cycles. After each cycle the roses should be pruned with clean pruners and cut back to a 5 leaf node with an outward facing bud. Cut off all weak and crossing branches. You want to prune to a vase shape. If you go to the American rose society page they have pruning basics. Certain types of roses will be pruned differently. The vase shape opens up the center to allow more air in and directs the growth outward. Do not prune more than 1/3 of the plant at any one time. If you have to wait a week for the plant to recover. Stop every once in a while to take a look. You can always come back to cut the branch later, but you can't fix it once it is cut off. You can adjust the shape at another time.
Feed the roses after they are pruned. Rose food or Miracle grow for acid loving plants, or citrus food (My favorite. I use it for most of my potted plants.)
Roses bloom on new wood. Dead head if the flowers don't drop off. (I usually buy roses that fall off cleanly). N
After the bloom, repeat what you have done.
At some point before the first frost you will need to winterize the roses. You need to cut them back to the five strongest canes, heel them in and cover them with mulch.
https://www.dummies.com/how-to/content/p ... amage.html
Happy gardening in Hawaii. Gardens are where people grow.