How do I help my dogs get along?

Dachshunds are great dogs. Especially senior dogs. All Dachshunds are great! No dog should ever be the "head" dog. You marriage marked a new member of the pack. They may get along great with your husband, but with a new member of the pack, they are going to try to establish dominance. I think it is wonderful that your coworker rescued a stray pup. Bringing yet another dog into the home is another member of the pack. If the dogs don't have a strong pack leader they will try to establish leadership themselves. Your dogs will only get along if you are the pack leader. Playing is always a good sign. A timid dog is an undersocialized dog. Puppies get bigger. They are now seeing the puppy as an adult and a true member of the pack, instead of a baby. Puppies grow up. You need to teach the puppy how to play nice and make sure you are exercising him enough. Never let a dog push another dog to get your attention. Tell him NO! They do not see you are the pack leader. Never let a dog guard anything! Sydney is hiding under the bed because she has no pack leader and she is undersocialized. Don't let the puppy bother the adult dogs and do not let any dog growl or show aggression. When they snarl tell them NO. Take them by the scruff of the neck and put them on their sides. Dogs are not meant to live seperately. When you put them on their sides while gripping their scruff, gentle get up. Do not let the dog get up until you say it is okay. Keep putting them in a submissive position until they stay there.