Mellsey, are you planning a commitment ceremony? Do you feel that this would be on the level of a group marriage? I've considered a group marriage, but I'm a little afraid I'd be jumping into it too quickly. Would you be replacing your wedding rings altogether?
Honestly, I like the idea of a claddagh--two hands holding a heart seems to sum it all up for me. If you're looking to have something made, perhaps you could all discuss symbols that you feel embody what makes the relationship special, or represent each of you.