Are 5 days enough for yoga in the week to stay healthy?
It all depends of what you mean by healthy, what type of yoga you practice, and how long you practice for, and what your practice consists with.
There are various types of yoga. Some are more dynamic and physically demanding; so, you'll likely break some sweat. They'll develop your flexibility, endurance, strength, and can develop some muscle tone. You can try Ashtanga yoga, Vinyasa, Power yoga for that. Other types are more passive and focus primarily on flexibility and relaxation, e.g., Restorative yoga, Yin yoga. Hatha yoga will be something in between.
In order to notice benefits, I'd advise you to practice a longer duration class (1h to 1h30min) at least twice a week. If you don't have so much time you can also have shorter practices, for example, 30min a day more often. 5 days of practice are definitely going to show.
Make sure you start your practice with a few minutes of quiet mediation to tune in, and spend at least 5 min in Savasana at the end, don't skip it.
As per the staying healthy part, yoga definitely will help, but don't forget about other aspects of your life, such as healthy and balanced diet, and enough sleep.