Astrology has nothing to do with gods
Astrology is the study of the movements and relative positions of celestial objects as a means for divining information about human affairs and terrestrial events. (Wiki)
You have actually created a circumstance were people are unlikely to believe in or practice astrology because it would be in competition with an established religion that has physical proof of its reality. Practitioners of astrology on your world would be quickly labeled blasphemers and driven underground.
People are people so why should it be, You and I should get along so awfully (Depeche Mode)
However, for your story to be realistic it must reflect the nature of living, reasoning, mistake-making beings. My own faith seems quite obvious and easy to believe — to me — but there are billions of people on the planet who don't understand it, don't "get it," and there are even those who don't want to. But to really make this behavior clear, let's look at it in a completely secular way.
People know and understand the power of the State. It's there, every day, in the form of governors (prophets), legislators (apostles), bureaucrats (evangelists), law enforcement (bishops), laws/ordinances/regulations (scripture), etc. (illustrative association with religious titles is my own and only meant as a simple example. No offense is intended.) We believe in this power, it is manifest, and even does good for people on the earth (police protection, welfare, etc.
And yet, there are multiple political parties because people have different beliefs in how government should affect people. No matter how well government manifests itself for the good of the people, there's always someone who wants to change it, replace it, or circumvent it. When we're impatient we violate the law and speed, when we're greedy we violate the law and defraud, we risk being caught by this very real, very organized, "religion."
For people to be believable on your world, you must accomodate those who, in the face of manifest power, will nonetheless seek to fulfil their own desires. They are outlaws in every sense of the word. People with divergent beliefs, mixed interpretations, etc. Some (call them "anarchists" for lack of a better word) who simply want to reject the manifest authority in favor of their own (or, quite often, in favor of simply wanting to be left alone).
You'd be surprised over the number of people who simply want no responsibility, who reject any and all authority no matter how obvious, how manifest, because they want to just do their own thing.
So, I understand that you don't want astrology in your world and, frankly, you've created as good a situation as I can imagine to avoid it. But remember, "people are people." There really isn't a way to stop them from believing in and practicing what they want. If you force your story otherwise, it will always read a little flat. You need to find a balance, because good and evil will always exist together.