With three arrests so far, dropping charges is what's known as 'enabling'.   He can't be forced to have a mental evaluation unless there are charges.  He can't be forced into treatment unless there is an evaluation that he is a danger to himself or others.

By enabling him to  continue with what is now violent behavior, the family is ensuring he will get no treatment until it gets worse.  The 'family' needs to understand that the next person he is violent with may reasonably believe that he is  "Committing or attempting to commit a felony involving the use or threatened imminent use of physical force against a person"  (like robbery).  

That's when a citizen or a police officer is authorized to use deadly physical force.