You might want to seek professional guidance for issues relating to this trust, particularly if there is no definite termination date and/or it is otherwise foreseeable that the trust will continue.
If the trust was initially a grantor trust (e.g., a revocable living trust) when your wife's brother was alive, then it most likely became irrevocable and a separate taxable entity upon his death. As a result, the trust should have an EIN (see link below) and file a Form 1041 if required.
https://www.irs.gov/businesses/small-businesses-self-employed/employer-id-numbers
Note that trusts are required to file income tax returns if they have gross income of $600 or more for the tax year or any taxable income for the tax year.
See https://www.irs.gov/instructions/i1041#idm140366311406240
