If your wife gave you and her mother a joint power of attorney over her and her assets, you did relinquish all rights and say as her husband. What was given in all likelihood was a "springing power of attorney" to you and your wife's mother to make decisions for her concerning medical assistance and her financial assets if for some unfortunate event such as a major accident, she could not make decisions for herself.Such powers to make decisions for your wife by you and her mother would "spring", or come about upon the happening of an event, typically a life threatening one.The joint power of attorney should state specifically when the powers are activated and the scope of the powers.Your marital rights as your spouse's husband remain under California law.