A will must be witnessed by two persons to be valid in all states except Vermont, which requires three witnesses. Each state has its own rule as to who can be a competent witness. While some states allow minors to witness wills, you should be sure that both of your witnesses are over 18 just to be safe.
The witnesses should not be people who are beneficiaries of your will. In many states, the witnesses can be beneficiaries, but it is better if they are not in case a question of undue influence arises.