Well, they're not very smart if they think one guy can pay attention to all three of them. I would say, if possible, confront them in a comfortable situation and make a joke about that very problem. A solution may present itself in the ensuing conversation.
On the other hand, if you absolutely do not want to be involved with them at all, then don't give them the notion that you are interested. You don't have to ignore them; ignoring people isn't nice. But you can make it appear that it's not going to work. Now, if you're really brave, then you can tell them no directly, in which case they'll probably scoff at you/deny that there was anything of the sort going on. Do that only if you're not looking to make friends.
As for C-zom, the thing that works best to inspire me is this: What's the worst that could happen? If you don't do it now, then it won't happen now. If you don't do it then, then it won't happen then. It's as simple as that. There's no reason to be wary of asking someone a question. If they think it's weird, ask them why they think so. If they can come up with a valid reason why it's strange to be a little aggressive, then concede the point. But all it takes is considering the negative effects. And if you get rejected, why be down? It's like if you asked someone to peel your orange for you, and they said no, except the positive result is so much better. It is worth it to try for something you desire.