Mom passed. 2 siblings, no WILL or any POA. The younger sibling was named beneficiary on mother's bank account. What can older sibling do?

In most jurisdictions, on intestacy (no will) assets are divided equally between children, so long as they are not otherwise disposed of. For example, joint real estate or a bank account in joint names automatically goes to the survivor, so it isn’t counted as part of the estate to be split equally. (Note - authority to operate on the deceased's bank account is not the same as joint ownership of the account) Payments relating to the estate (funeral etc) would normally be taken off the amount available to be split. I don’t understand what ‘beneficiary of a bank account means’, if it is not a joint account. The only way to change the legal split of the estate is by making an application to the court because of a need/ expectation for support from the deceased. Unless the estate is substantial and the reason for requiring support is clear, the legal costs of a court application are likely to make this uneconomic. If you have any doubts, consult a local lawyer.

Just go to mom's bank take her DL or ID & acct number and ask the teller if she had a beneficiary on her acct if she does & whoever's name is on it that money goes to that person & the court usually doesn't count this unless it's a big amount. If no name is on it than you will have to consult a lawyer.

So...

Your mother was part of a long-running workers' compensation claim case; and then, what, she accepted an out-of-court settlement? The money was duly paid and banked.

Your mother did not want your sister to know about this. Is that because she feared your sister would disagree with the decision to settle, or because she did not want your sister to know about the money, or both, or what?

Someone informed your sister, regardless. H'm. It seems to me that only somebody involved in the case could have done that; and it seems to me that if so your sister must have been actively involved in your mother's representation. In which case, it is possible that your sister not only worked hard on it but incurred some expense. Is it unreasonable that she would expect to receive a proportion of the compensation now that your mother is unable to benefit from it?

You paid your mother's funeral expenses. You can expect to be fully reimbursed for those from your mother's estate - it's almost a separate issue, and it is universally recognised as a legitimate use of a deceased person's funds. I hope you've kept all the receipts.

What should happen now is that your mother's estate will be valued. The estate will include all property, including your mother's personal belongings. Ideally there should be some sort of inventory taken. Was there one? Have you, at least, some idea of what the items that went mainly to your sister were worth in cash terms?

As your mother died intestate, the rule of thumb will be that her estate, after expenses, will be divided equally between you two children.

But unless the personal belongings have really significant monetary value you'd do better to ignore them, you know. It'll save a lot of time and bad feeling. I hope it's not too late for that.

If no will and there is an estate of any kind, you need to become administrator. Here, if under 20k an affidavit. Lets say Mom got 50k. All her debts have to be paid before any money is split. Funeral expenses, bills, taxes etc. You will need to do her taxes and anything owed will have to be paid. Your sister will not be able to get any money until you are sure all debts have been satisfied. That could take a while. Once done, then money can be split. If nothing left, oh well. Just have all your records of payments in order.