From the sounds of it, Teddy is displaying some fear aggression behaviors. I have some suggestions for helping him deal with this but I don't have time to post them right now. I will post later tonight or perhaps first thing in the AM. In the mean time, try to think back to when you first noticed him doing the things you mentioned. What age was he and how did you originally handle it?

One other thing.... Do you do obedience with him? This is very helpful in establishing yourself as his alpha leader. When you have littermates being raised in the same home, they tend to bond to one another as opposed to bonding to the human. You need to intervien here and make sure he sees you as the alpha.