It is not uncommon for cats to groom themselves and sometimes that includes chewing or biting at their tails. However, if your cats are doing this excessively or if there are signs of hair loss or skin irritation, it may be a cause for concern and you should consult with a veterinarian.

There are many reasons why cats engage in tail chewing behavior, including anxiety or boredom. It's possible that even though your cats live an easy-going life, they may still experience anxiety or stress for various reasons.

You may want to observe their behavior and try to identify any potential triggers or stressors. Providing your cats with plenty of environmental enrichment, such as toys, scratching posts, and interactive playtime, can help reduce boredom and provide mental stimulation.

Again, if you are concerned about your cats' behavior, it's always best to consult with a veterinarian who can assess their overall health and behavior and offer advice on how to address the issue.