Legal Question in Wills and Trusts in California

You should consult with an attorney. Contesting a will is very tricky. Based on what you said, you would have to prove undue influence by the sister. If she was an unpaid care giver for about 10 years, that may be difficult.

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Is your mother even deceased? You can't force people to change their wills and estate planning. Inheritance is a privilege, it is not a right. If she put things into a trust, there is nothing to probate, regardless of what a will says. If she executed a new will, and revoked the prior will, the new will stands until she revokes that one.