Peculiar transparent craft flying low no sound hovering over apartment near beach

Sitting outside looking at the stars on my back porch with my brother I saw the large dark craft coming towards us and over the apartment. While it was going over us it looked like it was changing formation and had an aura around it. When I first saw it was flying in a formation like a flock of birds, I couldn’t tell if it was multiple crafts or one giant one. It was really dark. It looked invisible. It was like flying very low like around 200 ft and silent. I know it sounds crazy…l’m hoping others saw it. It only lasted no more than 15 seconds once it went over the apartment we got up and checked the front it was gone.