You have a tough situation as it sounds like most of your mother's property was personal property with more sentimental value than monetary value. If there are cash assets and you at least know where they were kept (name of bank or other financial institution), you can open probate and secure those assets. With regard to your jewelry, you will either need to file a lawsuit in civil court to get it back or file a small claims case against your brother to get the value of the jewelry. You hopefully have a list of the jewelry and receipts or appraisals so you can prove your case against him. Good luck.
Consider doing a petition for intestate (i.e., no will) probate in your state. If you are named as executor or personal representative, you will be able to investigate what happened to your mother's possessions with the power of subpoena and the judicial process of probate. You mention that your mother also had properties in Mexico. If they are "personal" property, they may be subject to probate where your mother was domiciled at her date of death. If they are "real" property in Mexico, you should see a "Notario" in Mexico about the disposition of her property there.
You need to file a petition to probate your mom's estate, be appointed administrator and take control of all assets so that you make sure they are fairly divided. If you don't know how to do this, then find a probate attorney to assist.
I am sorry for your situation and for your loss.
The other attorneys here have provided you with excellent advice. You should consider filing a Probate Petition and request that you be appointed as the administrator of the estate. Acting as administrator with Letters of Administration gives you the authority to act on behalf of the estate and to ensure a fair distribution. Once appointed, and depending on the value of your mother's estate, there are other petitions that you may need to file, such as a petition under Probate Code Secs. 850 and 859. That type of petition requests that the court order an individual (such as your brother) to return property to the estate and also asks that he be liable for double damages.
I agree with Attorney James. As to your personal property, you may need to file a civil or small claims action to get your own property returned to you.
I would recommend that you speak with a Probate Attorney.
Disclaimer: The above answer does not create an attorney/client relationship. My responses are intended to provide general information about the question posted. I am licensed to practice in the state of California. The information provided on this site should not be used as a substitute for conferring with or hiring a competent legal advice from a licensed attorney that practices in the subject area in your state.