@duffycando,
If you wish to apply to probate court to be appointed the Executor of your brother's estate, you probably can do that--but you will need a probate attorney to assist you. And your brother's son may well challenge your application, and request that he be appointed Executor (something he may have already done). The final determination would be made by the court.
However, even as Executor, you must follow Texas law in the distribution of assets--and that will likely mean that the assets must
all go to your brother's son. You have no discretion in the matter as Executor--you must follow the law regarding the distribution of assets.
As Executor, however, you might be eligible to receive a small fee--which is determined by the court--for your services. You would be required to pay your brother's bills and debts from his assets, file all necessary personal income and estate tax returns, etc.