do ALL blood relatives have to state they do not have an objection to a will (daughter, brother) if they are not in it?

My mom wants me to sign POA to her lawyer so she claims, they can sign for me that I do not object to a will (that I have not seen). she says she is trying to put her house in just her name with out my deceased fathers. The house is in Aruba but he died in st. louis county MO where they used to live. she says all blood relatives have to state that they do not have an objection to his wishes, is that true? She has not asked his brother to sign anything, isn't that a blood relative? If I am not in the will, is there any reason for my signature/involvement at all?