When dogs are jealous of each other, the consequences are the same as they are for people. There may be some fights and if you let one pet dominate the other, you can end up with pets who bully each other.
Like us, dogs that live together have very complex interpersonal relationships. If your pets quarrel from time to time, that is only natural.
You can prevent jealousy by treating your pets equally and making sure they feel loved. Also, be certain that they don’t have to compete for their daily needs. That means no sharing of food bowls, water bowls, beds, and toys. Some dogs will share, but you can avoid issues by making sure they don’t have to.
All dogs have days when they’re grumpy – just like us! Also, even littermates will sometimes fall out. Try not to worry about the occasional quarrel but do step in if the growls and nips become snarls and bites.
If they go overboard, don’t smack! Just separate them and give them time to cool off. Then, when they’re all calm, act as a mediator by doing something you all like together, such as going for a walk.
After a one-off fight, dogs usually sort themselves out. However, if you have a situation where one dog is a bully, you need to watch out for signs and then run interference.
Dogs are very trainable so deflect unwanted behaviour with a firm but gentle “No”, and then encourage the behaviour you want.
While studying emotions is a challenge, there are some excellent theories and papers written on the subject. Charles Darwin’s The Expression Of The Emotions In Man And Animals is freely available online, and you need only Google “Emotion in animals” to find modern papers on the subject. But be warned, it’s huge tangle of a subject and fascinatingly addictive.