Is wisdom teeth removal necessary if they are not aligned properly. Can it lead to cavity or trouble in neighboring teeth?

Sometimes. Wisdom teeth can cause problems in neighboring teeth, including resorption, decay, and gum disease. These are more common when the wisdom teeth are not aligned properly in the mouth. When wisdom teeth even pose a threat to other teeth, it is best to get them out before any problems arise. Your dentist should evaluate your wisdom teeth and make a recommendation, so go see your dentist.
Maybe-yes-yes. If you can clean it, you can keep it. If you can't clean it, get it out before it damages teeth you need. See an oral surgeon or dentist with training in the complexities of wisdom tooth removal.