Each plant in its own pot, a couple of feet apart.

Bio advance
3 in one product.

I don't know where you live, I'm in upstate NY, and our growing season is short.
If you search "black spot on roses.site.edu" you should get research based info. Just look for your state.
In NY, counties have Cooperative extensions that have a wealth of info for individual growing areas tied in with Cornell University


https://www.gardendesign.com/how-to/black-spot.html#:~:text=A%20Cornell%20University%20researcher%20demonstrated,the%20spread%20of%20black%20spot.

To remain healthy. If you prefer an organic product, neem oil is a good alternative to protect roses from pests and diseases.

Also, the more sunlight they can get (with sufficient watering at the roots), the more able they are to withstand their natural enemies.

If you decide to replace it, certain roses are much better than others at fending off the enemies. One is Pinkerbelle. Knockout roses also have been bred to be resilient, but I don’t think they are very pretty (YMMV).