Your brother has an estate if he has a mortgage. You need to petition the probate court in your brother's jurisdiction to be appointed the Administrator of his estate. The court will issue Letters of Administration that will enable you to carry on the business of disposing of his estate.
Only if he is the executor of the estate and has court authorization.
If your brother is the sole owner and there is no outstanding mortgage then he has the right to transfer the property to you by a quitclaim deed. However, if there is an outstanding mortgage the lender can demand payment in full if the property is transferred. If the transfer is done to avoid creditors then the court can invalidate the deed.You should consult with an attorney who can check the title for any outstanding claims and encumbrances and then draft a deed that is proper for that jurisdiction.
The creditors will just have to write off the debt. You are under NO obligation to pay his bills. They will try to get you to do it, but you don't have to take it on.
Your children are the first cousins of your brother's children, and the first cousins once removed of your brother's grandchildren.
Your sister's husband is your brother-in-law. Your brother-in-law's brother is not related to you and neither are his children. But he is your sister's brother-in-law and his children are your sister's nieces and nephews.
Assuming the brother who died with a will was unmarried and had no children, and assuming his beneficiary brother predeceased him, his estate would pass to the children of his siblings. If he had only one brother then his brother's children would inherit his estate.
If your brother (or your sister) has children they are your nephews (males) and nieces (females).
Your brother's children would be your nieces and nephews.
Your brother-in-law's children are your nephews and nieces.
An Uncle
Your brother's child's children are your grandnieces or grandnephews.
Your dad's brother is your mom's brother-in-law. He is not related to your mom's sister or her children.