You do not declare your inheritance. A person who receives a cash inheritance does not pay tax on it and does not report it in any way.
An estate has to pay federal estate tax if the total value of the estate is more than a certain amount. For someone who died in 2019 the limit was $11.4 million.
Some states have estate tax with lower limits. A few states have an inheritance tax that is paid by the person who receives the inheritance. If your brother worked with a tax specialist I'm sure they covered all of this. I don't think you need to ask him anything.
