California  |  Wills and Trusts

family member taking control of mother's $$

My father passed away a couple years ago and my mother was left was a significant amount of cash. Recently, a family member has decided to take control of these funds and is slowly establishing accounts in his and my mother's name only (joint accounts). My mother has said she wants the money divided evenly between the children; however, with these joint accounts, is he the sole beneficiary? And if this is the case, what recourse do the remaining children have if any? There is no will or trust (except for the house). Thank you.