Typically, jointly held assets pass outside of the probate estate; the surviving joint owner takes all. However, there can be an exception to that rule if a spouse is involved.
Under most state laws, a person cannot disinherit a spouse. So, for example, a payable-on-death account cannot be used to get around this by putting all financial assets in an account and making it payable to someone else. In most states, the spouse is legally entitled to a certain percentage of the other spouse’s estate.
You will really need to speak with an attorney in your area who can advise you as to your rights under specific state law.