The following is not legal advice for your situation, despite the occasional use of the second person. Rather, it is general commentary about how wills work.
There are four good options: (1) do it yourself (2) hire a lawyer ($200 - $3,000) (3) use a legal forms service such as LegalZoom.com ($30 - $100) (4) buy a how-to book from a company like Nolo ($15 - $40)
If you do it yourself, you will need to think about what you own, decide who you would like to get that stuff when you die, and then write your instructions down on a piece of paper. You should then find two adults who are (a) not your relatives, and (b) not mentioned in the will to be your witnesses. Reassure the witnesses that you are sane, thinking clearly, and acting of your own free will. Then sign the will by writing your name in both print and cursive at the bottom. Add today's date. Then have each of your witnesses do the same. Have the witnesses write "witness" next to their signatures. Finally, make two photocopies of the will. Keep one in your desk for handy reference, give one to a friend or family member for publicity, and put the original in a safe deposit box at a bank for safekeeping.
If you decide to hire a lawyer, make sure the lawyer speaks a casual dialect of English in addition to legalese -- a will that no one but lawyers can decipher will irritate your relatives. For free, you should expect to be able to briefly discuss what sort of will you want. After the discussion, insist on a flat fee that will cover drafting (writing), execution (signing) and an uncontested probating (publishing and enforcing) your will. Do not agree to an hourly rate unless there is a firm cap on the number of hours. If your relatives challenge your will, you will probably have to pay additional fees. If you think this is likely, set aside some money in your will to pay the legal expenses associated with publishing and enforcing your will.
Have the witnesses write "witness" next to their signatures.
Is it actually important that the witnesses be the ones to write "witness"? If so, why?
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)