I'm sorry about your husband's death. If your husband has a will that he prepared after you and he were married, then that will governs who is entitled to what. If he did not have a will prepared after you were married, then under California law you are entitled to all of the community property and 1/3 of his "separate property". In either event you are entitled to all of the "joint tenancy" property and bank accounts that were in both of your names.
If your husband and you had any community property that is being probated and he did not have a will, then you are entitled to "first priority" to be appointed as the "administrator of the estate". You will need to file your own petition contesting the petition filed by your stepdaughters.
By all means, see an attorney as soon as possible to determine your rights!
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.