Is my husband entitled to see full disclosure on how his sister is managing his mother's estate?

A trustee has a duty to provide an accounting to the beneficiaries. The beneficiary also has certain rights to challenge things listed on the accounting. Specifics on the beneficiaries' rights to request an accounting vary from state to state. If the trustee does not voluntarily provide the accounting, then the beneficiary's remedy in California is to petition the court for an order that the trustee provide the accounting requested. In theory, a beneficiary can do this without a lawyer, but I would not recommend it. I have seen far too many people try to represent themselves in court and make mistakes that harm their case. The court likely would have no problem granting the order, assuming the beneficiaries have indeed informally requested an accounting and the trustee has refused. I would consult with a probate lawyer about these matters. I know that I have represented people in rust matters with relatively little money up front, and a promise to be paid upon distribution from the trust. I also would be happy to discuss this with you, to provide more information as to your rights and the costs involved.

Your question is a bit ambiguous. "She established a Trust that eliminated both [h]er brothers and put her own daughter in place should anything happen to her." Is "She" your sister-in-law? Or is "She" your mother-in-law? Is your mother-in-law dead? Apparently you have a copy of the Trust, and a lawyer said that your husband is a beneficiary. If your mother-in-law is alive and established the Trust, and the Trust is revocable by her, then your husband probably has no rights. If your mother-in-law is dead and established the Trust, then your husband is entitled to be kept reasonably informed of the Trust's existence and the Trustee's activity. Normally, this mean he gets an annual accounting and report. If your mother-in-law died less than a year ago, then do not expect detailed information very soon. If your mother-in-law died recently, know that you have a very limited amount of time in which to challenge the trust. If your sister-in-law is the one who established the Trust, then how did she do that with your mother-in-laws assets? I recommend that you should not represent yourself.

The lawyer you consulted was correct. Obtain the services of a probate litigation lawyer to compel an accounting... Assuming your mother has passed, and your husband is one of her sons, beneficiary, he can compel an accounting of all of the funds; but a lawyer is going to be required to hammer your sister in law into place and provide your husband the accounting. By the way, POA died when your mother died. I am a little uncertain here if your husband's mother has died; if not then the POA is alive and may put a different complexion on this matter.

If your husband is a current beneficiary then he has the right to information. If he is a contingent beneficiary he may not have the right but if he has proof of the undue influence then he should pursue a court action while there are still assets to be saved.

You don't say whether your mother-in-law is still alive. I presume she is since you got a copy of the POA. Was it really your sister-in-law that established a Trust or was it your mother-in-law? If your mother-in-law is still alive, is she competent? If your sister-in-law is the Trustee of your mother-in-law's revocable trust, then your sister must account to your mother-in-law and not to your husband... until your mother-in-law dies and the trust becomes irrevocable. If your mother-in-law is not competent, then perhaps a conservatorship should be started and then your sister-in-law would have to account to the conservator and that information would be available for your brother to review. If there is some undue influence or lack of competency to execute an estate plan and your sister-in-law had an attorney prepare something that benefits only her, then that would be able to be challenged. Perhaps it is elder abuse and should be complained about now. Only after your husband is a beneficiary, rather than having a mere expectancy, would your husband be entitled to an accounting and getting information as to the Trust and what is going on.

Why do you doubt what your attorney told you? You are the type of client no attorney wants. Your lawyer was quite right.