Parallel operation of solar charge controllers, engine alternators, gensets running shore power chargers, etc. is possible and usually works ok. Each device will have a different, sometimes a lot different charging parameters. When the batteries are low then all will put out near maximum, unless it is too high a percent of the batteries amp hour capacity. That limit is usually stated as 25% for FLA batteries, maybe double for AGMs.
As the batteries become more fully charged, say about 75%, one or more of the devices may switch to float, but that is ok because at that point the batteries can accept less current anyway so it doesn't matter.
But if I had my druthers, I would have one large solar controller rather than two in parallel.