Please consult a guardianship attorney. As a wife, you should have priority over your husband's siblings. Also, if you live in California - which it appears you do - it is a Community Property State and you have specific rights. You need to contact an attorney ASAP.
Ms. McMahon is right. You are well advised to seek a local guardianship attorney right away.
Rani K. Sampson (509) 663-5588 is a Washington attorney whose clients ask her to solve problems and negotiate difficult situations in real estate development, business formation and operation, estate planning, probate administration, and other matters. All answers are for educational purposes and no attorney-client relationship is formed by providing an answer to a question.
In California, you seek a Conservatorship of the Person and/or Estate of an adult. My colleague is correct in that you should have priority as the spouse. You can start by having his doctor complete a Capacity Declaration (GC-335). You can find the form on http://www.courts.ca.gov/forms.htm. But, you must have an experienced conservatorship attorney help you with this immediately.