"Oral" is a word usually used to refer to something that goes into the mouth. Like an oral medication. You could ask, "Can someone help me make this sentence sound more natural?" As for your sentence, Adaeze gave you one option, though with an interpretation of "realize" as a mental concept. I don't believe this is what you intended. Here is an interpretation of "realize" as a manifestation: When people and animals live together in harmony, they will realize a sustainable ecosystem. However I would further refine it to: When people live in harmony with nature, they will finally realize a sustainable ecosystem.

People will realize that living in harmony with animals will eventually develop a sustainable ecosystem