By all means, consult a lawyer in planning and writing your will. If your will is not executed as the law prescribes, or if it attempts to do illegal things, it may be declared invalid. An untrained person is likely to use inaccurate or ambiguous language in drawing his will that when contested would be subject to the interpretation of the courts.
A lawyer is equipped by training and experience to help accomplish what you desire. Tell your lawyer what you want done and allow him to put your wishes into draft form and have him explain the language and effect to you. Careful thought should be given in drafting a will. Remember, at the time the will goes into effect, you will not be around to explain what you meant to say.