Everyone usually has an idea about harmony.
Something that sounds good, in the groove, or just blends well,..this is different for some but generally “we” might agree on interesting intervals like fifths making that pleasurable sound experience.
After I had been studying with him for two years, Schoenberg said, “In order to write music, you must have a feeling for harmony.” I explained to him that I had no feeling for harmony. He then said that I would always encounter an obstacle, that it would be as though I came to a wall through which I could not pass. I said, ‘In that case I will devote my life to beating my head against that wall.’ ~from silence by John Cage.
With each member here comes the harmony that they like either from experience in playing or listening or yet simply being exposed to something that at the time was enjoyable.
Mixing harmonies can get intangibly monotonous or just difficult to everyone participating BUT
Creating a new harmony is a kind of paradigm with sounds in a syntax and format we are making now.