life estate

What is the name of your state (only U.S. law)? california
My brother granted himself a life estate while acting as trustee to my mothers trust and deeded her portion of the home and property that she and I owned in joint tenancy for thirty years, to my other brother and my sister. My mother deeded the property to her trust as her sole and seperate property to keep it from going to my step father but she didn't sever the joint tenancy with me according to cc683.2. My question is: can my brother will his life estate to his ex wife after he dies?

I presume that the transfers your brother did as trustee were consistent with the trust (you don't seem to argue that) including the life estate. The life estate expires with him. He can allow others to use it while he is alive (even renting it out) but it ends on his death. The "Joint Tenancy" (if one truly existed when the property was transferred in to the trust), most likely turned to tenancy in common when the property was transfered out of the trust.

Assuming for the sake of argument, that the property was in joint tenancy with me when my mother died,and I know it was, how is it possible for the trustee to change the ownership from a joint tenancy to a tenancy in common after the death of the joint tenant grantor of the trust by deeding the property out of the trust? Joint tenancy is supreme in all matters regarding wills, community property and trusts. Am I missing something? When my mother died she was a joint tenant with me in the property. Isn't the trustee required to quitclaim the property out of the trust to me as the surviving joint tenant regardless of what the trust says? Isn't the trustee required to quitclaim the property out of the trust to me as the surviving joint tenant? By not doing so, isn't the trustee committing a slander of title? Before my mothers death my brother tried to change the title to tenancy in common while the property was in the trust and using his power of attorney but the county assessor refused to accept the change as he was not the grantor of the trust and was not on the deed and my mother refused to sign the quitclaim.