State law can change a will also. This is commonly done when there has been a divorce. Usually a divorce terminates the ex-spouse's rights under a will, unless a contrary intent is clearly shown. A separation doesn't terminate a spouse's rights under a will. The specific impact of divorce on an existing will depends entirely on state law.
You won't be able to avoid protections given to others by act of law, either. This can include your spouse's rights against the estate, community property protections, and special protections for children.
Having more than one representative can create problems during probate, however. Normally they will have the same powers to act, and this can create conflict. The nomination of two or more executors/representatives should be carefully considered.
Appointing co-representatives might be an emotional reaction - not wanting to hurt someone's feelings. However, an emotional reaction is often not the best choice for a legal situation. If you nominate co-representatives, you need to believe that they will be able to cooperate in handling the estate.
You must have grounds to have a chance of successfully contesting a will. Unhappiness with the proposed distribution of property is not a valid ground. Valid grounds depend on state law. Incapacity, fraud, undue influence and duress are the most common grounds.
There are tax implications and simple ownership issues for a joint tenancy.
A joint tenancy is not the equivalent of a will. A will can do a number of other things. A joint tenancy creates a situation where the other joint tenant will get the whole property at the decedent's death. But if you give your brother Bob an interest in a joint tenancy on your home, Bob could sell his interest or his creditors could go after his interest.
Along the way there may be other necessary actions, like selling estate property to cover debts or allow for proper distribution.
The testator normally must have attained the age of majority, and must be of "sound mind" at the time the will is executed. A married minor is usually capable of executing a will.
The witnesses normally MUST be "uninterested," meaning they're not beneficiaries of the will. Witnesses also must be competent persons.
A will normally doesn't need to be notarized, but a document called a "self-proving affidavit" might be created to provide further legal strength to the will.
"Holographic" (handwritten) wills are still recognized in many states. Such a will must be in the handwriting of the testator and signed by the testator. Witnesses aren't normally required for a holographic will. State law might impose other conditions on a holographic will.
As part of the probate process, the creditors of the decedent get first shot at the estate property, after certain allowances for a spouse and children.
Someone who leaves behind a girlfriend or boyfriend, or even a fiance', will not be able to provide them with any inheritance unless there is a valid will. There is almost no exception in the law to provide otherwise.
Kits for writing a will are normally not state-specific. If your will fails to follow state law, it will be invalid.
Many states have provisions for an "informal probate" which greatly reduces the requirements of interaction with the court, but doesn't eliminate the court entirely. Most every estate will have a piece of property that passes by title or deed, like a car or real property, and normally only someone with legal authority can legally transfer such property.