If your parents owned any property, had any money, someone had to probate their estate, with a will or without one;  if there was no will, the law of intestate succession would require an equal division of the net estate among the four of you.

You should be able to find out form the probate court, for the county of your parents' last residence, about the probate of their estates.  An attorney who practices in the area can help you with this, and with whatever turns out to be necessary once you've seen the records.  If you've been deprived of your share of the estate or estates, you can sue, and the executor or administrator who did this can be held personally liable.

In California, a Will must be filed with the probate court in the county where the decedent resided within 30 days of the time of their death.  At that point all beneficiaries should be notified. Additionally, once filed, it becomes a matter of public record and anyone can request a copy (whether or not a designated beneficiary). 

If there was no Will then the deceased is said to have died "intestate"; accordingly state intestacy laws would apply.  In this instance, the estate would be distributed to the heirs (ie children) equally. 

However, depending on how assets were held, they may or may not become part of the estate so a probate proceeding may not have been required.  For example, accounts jointly held, assets with "payable on death" designations, or the like. Again, you can check with the applicable probate court as to this.

You should also consult with an estate at/family law attorney as to your entire situation.  In the meantime, here is a link to a site that I think you will find to be of help:  http://www.scselfservice.org/probate/prop/FrequentlyAskedQuestions2.htm#long