I amnot licensed in CA so can only answer in genneral terms. If both parents died without a will seven months apart, boh pobate esates would pass in accordannce with the CA intestate statute. Since your father died first, any community property would likely pass to your mom. Her estate would pass to her heirs. If you and your brother are the only children and there were no other children who failed to survive the parents who left grandchildren, the probate estate would be split equally between the two of you.
However, some assets are non-probate and pass outside the intestacy statute authomatically by operation of law. You would ned to closely examine the title to the house and car to determine whether or not your mom used them to create a joint tenancy (with right of survivorship) with your brother. If she did, they pass only to him. If not, the titles created a tenancy in common and her interest passes under the intestacy statute. Even if there is no joint tenancy, there would have t be a determination of what the intent and consequences of the re-titling was on your mom's part, to determine what, if any, interest your brother already owns. Was a giftintended? Was it reported as such on the real estate transfer tax form? Did mom file a Form 706 gift tax return with the IRS?
Finally, to the extent your brother did actually provide care for your parents, he would have some sort of creditor claim against the estate (offset by the value o living at the home rent free). You should seek to arrive at an equitable arrangement with your brother that takes his service into account. As you can see, the legal issues will otherwise be thorny and expensive to untangle.
I am assuming that your mother lives in California and that you live out of state. If that's not the case, then my answer may be incorrect because the answer depends on the law of the state where your mother resided.
The first question is exactly HOW your mother added your brother to the title. If it was Joint Tenancy with the Right of Survivorship, then the house would automatically pass to him upon her death. Even if she had a will, the joint tenancy would control the outcome. He would get the house in its entirety. If she was on Medi-Cal, then that pretty much means that she didn't have any other substantial assets. So, that might be the end of the story.
Now, there is an argument that can be made that your brother used his caregiver relationship to influence your mother to divide her state unequally. If the facts support it, you might be able to pull the house back into your mother's estate so that it could be divided equally. Of course, doing so would also subject the house to Medi-Cal reimbursement as well.
I would suggest that you check with a lawyer to make sure that the outcome I described above is what would actually happen. It's certainly possible that the house was held by your mother and brother as tenants in common, or that there is some defect in the deed, etc.
If it does turn out that he gets everything, you might want to horse-trade a resolution, especially if that's not what your mother would have wanted. You can ask him to buy out your share of the estate by making monthly payments to you or some other such arrangement. If you do that, just make sure that the agreement is that he is settling your claims against the estate, not that he is purchasing your share of the property. There are potentially significant property tax issues if he buys your share of the house.
There are a number of important issues that are raised in your question, all of which will determine the final answer. The only way to know for sure is to consult with an attorney in California.
1. If you mom received Medi-Cal, whatever property she held at her death, may be subject to recovery by the state.
2. If your parents (or your mom) transfer title to your brother as Joint Tenants, it is an all-or-none transfer and the survivor takes all. If it was transferred to him as Tenants in Common, then your mother's share would be divided between you.
3. If your mom's total estate was under $100,000 it would not be subject to full probate, but if the real estate was valued over $20,000 a summary proceeding would be needed.
4. The Intestate Succession (no will) statutes do provide that the decedent's estate would be divided in equal shares between the decedent's issue but nothing is black and white in the law and you need to gather as much information about your mother's holdings as you can and then consult with an attorney.
This is general advice and is not specific to your particular situation.