Wills

Dear Len & Rosie,

I am unmarried, I have no kids. I own a home and a vacation rental. I have written a will in case I die unexpectedly. Does a will have to be witnessed? If not, is it completely invalid? Do I need an attorney to hold onto the will to make sure that it is implemented? Is there any difference between having an attorney implement a will and having a brother or sister implement the will?