You can indeed romance multiple characters. Unless I am wrong, Hyao believes in polyamory xD (in a fantasy world at least). However I dont know what extent of content there is for Airon and Hayden. Maybe someone else can help with that.
Ah okay thanks. I'm not sure i understand what u mean by polyamory, but it is nice to know that we can romance not just 1 character. Personally, its exciting to see how much content a game has to offer by exploring various options