The best on-line estate tools and research articles are from Nolo Press, which specializes in this area. BUT: those here who are pointing out state laws are not consistent from one to the other, are entirely and completely correct. State law guidelines MUST be followed or you invite trouble.
Never expect multiple heirs to "play nice" with one another. If your estate is over $50K plus OR involves RE ownership, especially joint, you need a will and other attendant documents. $50K is not a magic #, btw - it's merely most states and the IRS don't care about small estates with modest net worth.
Anyone who has IRAs or 401k retirement accounts should discuss with their tax advisor how to have the heirs aware that very specific IRS guidelines need to be followed or they will be in a world of tax pain - and the IRS doesn't let you 'backtrack' a mistake unless you correct it within hours.
Living Wills have been superseded by what is called the Healthcare Power of Attorney doc. It should be discussed with your doctor, who signs it, and keeps a copy. You need a signed copy for your records as well. Whoever is your Agent AND Successor Agent should also have a copy. This is because of the HIPAA (Privacy) law. If you are in an accident and land in the hospital unable to verbally and coherently express your wishes, the medical staff must have that HPoA on record to speak to your Agent or Successor Agent.
Yes, if you're in a small town and "everybody knows everybody else", this can be discreetly ignored - but medical staff have been sued for violating the HIPAA law, so better safe than sorry.
Be aware that in regards to wills, state law can be very specific about who inherits if you die intestate (without will or trust), and therefore if your will disinherits any of those people, it can be challenged. For example, a house may be in your name entirely. Try to pass it on to your children, bypassing your spouse by assuming a verbal agreement to remain until spouse's death or move-out - but it can be legally challenged in states where the spouse is automatically assumed to have a share from one-third to one-half of a person's estate.
Best to have an estate attorney's advice for your will. The Healthcare PoA is a standard form and Nolo (and other websites) have state-specific forms you can download.
Always remember any time one of your Agents or Heirs passes away or cannot serve, to update your documents, too!
