Who should be the POA?

My observation is that there may be some very valid reason, given the wrongful death lawsuit, for the Power of Attorney to remain, as your foster sister's lawyer says, with the son. I do not see it from what little information you post, but if you think you have some rights about something that are being violated, then contact a lawyer in your locale, talk things through (many in your area might do a free consultation) and put your mind at ease.

Good luck to you.

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I am having difficulty understanding your post. In my state a POA ends with death, and only the administrator ad prosequendum and/or executor of the estate can go forward with a wrongful death lawsuit. These suits are complicated and difficult to win, but many times the person who brings the suit has very good reasons for doing so. You might find my legal guide on medical malpractice helpful. If this is her husband, why did the money from the life insurance proceeds go to the children and not her? Was she a named beneficiary? Also the boyfriend has NO legal say in what is done with this estate. Why are her children managing something which she should be doing UNLESS she has been declared incompetent? She should sit down with a lawyer and get some answers.
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Mr. Sarno is licensed to practice law in NJ and NY. His response here is not legal advice and does not create an attorney/ client relationship. The response is in the form of legal education and is intended to provide general information about the matter in question. Many times the questioner may leave out details which would make the reply unsuitable. Mr. Sarno strongly advises the questioner to confer with an attorney in their own state to acquire more information.

I do not understand.

When a person dies, the POA dies with them.
Only a court appointed executor or administrator can have the power to pursue the claim.

Am I missing something?

I do practice in Massachusetts.

The other Massachusetts attorney is correct. Your foster sister's husband cannot have a Power of Attorney because he is not alive. The appropriate person to bring a lawsuit for wrongful death on behalf of your foster sister's husband is the executor or administrator of his estate. I would advise you to speak with a new attorney.