If they put pressure on you to pick a "best buddy," try to maintain a neutral posture. It's not fair of them to attempt to make you choose a best buddy, and you don't have to simply because they say so. Then ask them which one they would like you to be. You can also tell them that you are not looking for friends but instead want to become more acquainted before deciding what role you will play in their lives. If they still insist upon your picking a best buddy, then do your best to stay neutral in the relationship. If they feel rejected or ignored, they may decide to stop confiding in you entirely. So always make sure that you aren't coming off as being too eager to join their team. In conclusion, don't feel obligated to pick a best buddy just because they ask you to. And even if you were to select one, it wouldn't matter unless they want you to be their friend.