Some groups of dogs get on wonderfully well, and sort out their differences with little fuss. Other dogs are too pushy for their companions to deal with, and need more intervention from you. It helps keep the peace if newcomers are encouraged to respect resident dogs, and if you give privileges for good behaviour rather than for a dog looking cute or being pushy.
Pushy youngsters may benefit from a little discipline from older dogs, if it teaches them to behave better and accept the oldster's authority. However, all dogs that live together need to respect a 'no fighting' rule, it's safer for them and for you. If they scrap, you can scold the dogs involved without taking sides. This may leave you with your best behaved dog retreating from a pushy dog every time he is provoked, in order to avoid a fight. Your best behaved dog is not showing weakness, on the contrary, he's showing self-control, and deserves more privileges than the pushy dog. Pushy dogs can learn to copy well-behaved dogs if they see that being well-behaved, eg sitting and staying on command brings rewards. Then the penny drops, and they start watching the well-behaved dog to see what they are meant to be doing to get the rewards you give.
Prevention is important if your dogs have a tendency to squabble. Always supervise meal times, and increase the distance of feed bowls from each other if the dogs behave badly. Be careful about how you allocate chews, because dogs will sometimes squabble over chews left on the floor. Recognize signs that a fight may be brewing, so that you can prevent it with a command or a distraction. Putting dogs in a 'down' when you arrive home may help if they all want to greet you at once, and might squabble over who gets to you first. If you have to stop a fight, keep your distance, so you don't get bitten, and use whatever is at hand to distract the dogs, like turning on the vacuum cleaner, using a water pistol, or a bucket of water if you are outside.
Some people don't ever allow playfighting, which is different from real fighting in that the dogs use playbows, and aren't trying to hurt each other. Dogs vary in how far they can playwrestle and chase without it getting out of hand. It's safer to ban playfighting indoors. Precious objects can get broken, it can get out of hand, and you are entitled to peace and quiet.
It helps to choose new companions carefully, so that they are likely to fit in with your existing dogs. The better suited they are to each other, the easier life is for you. It’s safer not to leave a newcomer unattended with your other dog or dogs until you are sure that they get on very well. Again, if despite your best efforts your dogs are not respecting one another, get help from a professional with a lot of experience of solving this problem.
