You need to think about the direction of the light when you bounce.
Bouncing isn't just about pointing the flash up, or up and forward. It's about picking the direction of your light. If you're bouncing, you have to stop thinking of the flash as your light source, and think of the reflecting surface your flash is pointed at as your light source. In other words, point the head of the flash at where you'd put a softbox in a studio. In this specific case, you put the light in the ceiling, straight over your head, more or less pointing downwards.
If you want the light to come from the front more, you need to bounce behind you. But there may not be a reflective surface (wall) there. So, choosing where in the room you do this, and how the room is shaped / how far away the walls/ceiling are all key. The higher the ceiling, the less liable you'll be able to bounce, because light, like all forms of electromagnetic energy, falls off according to inverse square. (1/x2). Double the distance, you quarter the light; triple it, and you've down to one-ninth. There are reasons to still use a high ISO setting, even if you use a flash.
You may need to set up a reflector or reflective surface, or rearrange where the group is standing, so you can use a bounce surface. Or. Consider taking that flash off camera, and remotely triggering it somehow (most commonly, with a radio transmitter/receiver).
See also: Neil van Nierkerk's Tangents website. He's got a ton of information on bouncing an on-camera flash.