You need a family lawyer. Grandparents in CA who have a relationship with the child may have visitation rights, but the parents are presumed to know what's best for the child, and it's the parents (and the child's best interest) that the courts will defer to.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Although I agree with the previous post, you would need to file in the court where your daughter was given custody (and I'm assuming that even though the father actually has physical custody of the children, he didn't go to court to change it legally because you say "daughter has custody").
You would need to file what is called an Order to Show Cause but it is complicated because you aren't actually a party in the case so you should contact an attorney.
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