siblings sign a quit claim deed to their brother. Brother dies without a will. What is the siblings obligation at this point

Based on the few facts you have given, and without any other information, the property is owned by your brother's estate. The Estate would be "responsible" for the property. Your brother's heirs would be the beneficiaries of the property. This is a very simplistic answer. There are many possible facts that might be relevant to the question regarding who might have an interest or a claim in the property. If you want a definitive answer, you should meet with an attorney who can ask questions and give you a more specific and definitive answer to questions and, perhaps, raise questions you have not even asked.