do i have a right to my mothers 401 whom passed away in may 2019 my step father was her beneficiary but he passed away in the 90's & she never changed

  There is a good chance that under the rules of the 401(k), a beneficiary has to survive the deceased and, if not, the estate of the deceased is the beneficiary.   This would mean that you need to open a probate estate for your mother, and the money would flow according to her will or, if there was none, in equal shares to her children (if she died without a spouse), after payment of administrative expenses.   You need to first check with the people who administer the 401(k).

  There is a good chance that under the rules of the 401(k), a beneficiary has to survive the deceased and, if not, the estate of the deceased is the beneficiary.   This would mean that you need to open a probate estate for your mother, and the money would flow according to her will or, if there was none, in equal shares to her children (if she died without a spouse).   You need to first check with the people who administer the 401(k).

No.  If there was no contingent beneficiary and your stepfather predeceased your mother, her 401k will pass to her estate.  After her debts are paid you may receive some monies if you were named in her will or, if there was no will, are an heir at law.  Her estate must be probated.