State laws offer differ on many points. To get a correct answer to your question, you should contact a California attorney. I am puzzled by the fact that the attorney says this is the "kids' lawsuit" but has not answered your questions. I would suggest clarifying with this attorney precisely who the "clients" are that he or she is representing.
Your mother's pending lawsuit became her estate's lawsuit when she passed. As one of her children, you would seem to have standing to review both your mother's wills (your other post refers to two of them) and the progress of the lawsuit.
The foregoing is for general information purposes and does not establish an attorney-client relationship.
Your facts are unclear. If mom had a PI case going and then died as a result of the injuries, her estate could sub in as Plaintiff. There are certain damages her estate could seek, which are different from the damages available in a wrongful death claim by her children or spouse.
There are tactical reasons why it might be better to not have the estate make a claim. These are complex issues that need to be properly considered. You need to clarify with the other atty who her firm is representing, the estate or your siblings or both. If there is a probate case opened you should be able to get a copy of the will.
The probate case may have nothing to do with the wrongful death case, depending upon other assets/debts etc your mother may have had.
If mom had lots of creditors, you dont want the estate to recover money in the death case, as it will go to creditors rather than the children.
I am so sorry for the loss of your mother, first off. Second, if your mom hired the lawyer, then the lawyer had an attorney client relationship with her. There may be practical and technical problems for the lawyer and his/her ability to act with full authority in that lawsuit if there was a will, or not one. The lawyer can give you a meeting, but may feel hamstrung about giving you information that may otherwises be privileged until an estate is established. To be most sure, I would hire my own lawyer to help you sort through this and then assist in your communications to that lawyer. It does not have to be adversarial. Right now, that lawyer knows the most about your mom's case (presumably). Undue influence (which you allude to) is a big allegation and no one can begin to assess that based on what you have said here. Undue influence could only apply if there was a will change, and you don't even know that for sure. This is cumbersome, but with good advice you can work through it. Hire a good lawyer soon.
The answer provided by counsel in the AVVO forum is not intended to create an attorney-client relationship. The information is opinion only and given free of charge without full understanding of all facts and the law applicable to any question-poster's individual circumstances. The best advice is to take the question from this volunteer forum to a more formal communication with a practitioner in the specialty area indicated by the nature of the claim.
A roundup of the best tips and legal advice.