New puppy issue... please help!!?

I just got a new Schnoodle puppy 5 days ago. He is barely 5 months. He is overall a very happy, healthy, cuddly, playful pup. So here's the problem. I am a huge Cesar Millan fan and so I knew right from the start that he needs to know that I'm his leader by giving calm-ertive energy. It worked... with me. The problem is that he only trusts me now. When my fiance, my mom, or anyone else in general tries to interact with him all he does is bark, growl, shake, and either try to hide. I tell him "No" when he barks, and I praise him when he relaxes but as soon as someone stands up or moves he starts barking again and at times he even nips at pants -- sometimes at me too. He barks at just about everything and everyone - usually* not at me though. I don't know what to do about this. I refuse to let him be one of those annoying controlling little dogs that I've met, I just don't know how to train him to stop. It almost seems like he has low self-esteem. How can I help him be more trusting?