How do I stop my dogs from attacking each other?

I currently have 3 dogs living in my house. I have a big golden doodle and medium sized terrier mix. My terrier attacks my labor-doodle very viciously to protect what he thinks is his. Today my terroir snapped at my labor-doodle. I tried to break it up and my terrier ended up leaving two deep puncture wounds in my arm. He has snapped at my labor-doodle about 5 times now and bites him hard. It is a very difficult altercation to break up. My labor-doodle doesn’t fight back.. He gets very scared and hides in the corner for days after. Our terrier also gets angry with the other people living in the house. He growls if you do something he doesn’t like. He has bitten 3 people in our house in the face. We try to punish our terrier but he doesn’t seem to understand and he keeps doing it. We were thinking about trying a shock collar but are hesitant. Do you guys have any other suggestions to stop him? Or should we try the shock collar?