The only way you can ensure that your assets will go to those people you wish to benefit from your estate is to have a will. Everyone over the age of 18, or who is married should have one.
If you do not make a will, you would die "intestate" and your assets, along with personal possessions, will be distributed according to the Succession Act. Your assets could therefore go to people you do not wish to benefit. Intestate estates are generally more complicated to wind up and, consequently, the associated costs are higher.