Cats can become jealous when they feel they are being excluded or their environment has changed drastically or suddenly.
Causes
Sudden changes. It may be the arrival of a new family member, such as a newborn baby or pet. Cats are not happy when their owners are being more attentive to other humans, pets, or even inanimate objects.
Lack of socialisation. It may lead a cat to become too clingy and show signs of jealousy at times.
Lack of bonding time. As much you might like to, you can not engage in playtime with your cat 24/7. When cats feel like they are not getting enough bonding time with their owners, they might display jealous behaviour.
Lack of personal space. A new family member - whether a human or pet - may have inadvertently taken away from your cats' preferred parts of the home and could also be the trigger.
Signs
Urine marking. Some cats deal with jealousy by urine marking.
Aggression. A jealous cat can be more aggressive and start scratching or biting.
Depression. More reserved cats might ignore their meals or hide away from everyone.
Solutions
Understand the causes of jealousy. The first thing you need to do is determine what exactly is provoking jealousy behaviour in your cats. Once you figure out the cause, you can address the problem.
Give your cats lots of attention. Simply bestow ample amounts of attention on your cats and make a point of interacting on a routine basis. The extra attention can curb jealous behaviour.
Give your cats personal space. You can also manage jealous behaviour in cats by making sure that new pets do not gain access to their belongings and preferred spaces.
Last but not least, show more love to them. Let your cats know that although some things are different now, you care for them just the same.